Ten year contract for seasons 4-13: 191 batters considered 1903-2018.

Year four is when a player is now eligible for salary arbitration and some big bucks three years before becoming a free agent. For a really good player, his team might want to sign him to a long term contract.

Current conventional wisdom is that ten year contracts are too long. Free agents Manny Machado and Bryce Harper just signed for ten and thirteen years respectively. Both are entering age 26 season.

What if current rules existed since 1903? How many batters would have been productive for ten years? More than you might have thought. Data from baseball-reference.com

Note post written the next day:
baseball-reference.com baseball-reference.com defines first three seasons literally. Monday, March 11, 2019

191 batters made this list:

1903 to 2018, From 4th season to 13th season, (requiring OPS+>=125 and At least 5000 plate appearances), sorted by greatest Adjusted OPS+

Rk	Player	OPS+	WAR/pos	HR	AB	PA	From	To	Age	G	R	H	2B	3B	RBI	BB	IBB	SO	HBP	SH	SF	GDP	SB	CS	BA	OBP	SLG	OPS	Pos	Tm
1	Babe Ruth	215	87.7	349	4181	5328	1917	1926	22-31	1236	1090	1471	296	86	1061	1065		693	29	51			85	79	.352	.486	.714	1.200	*79/183H	BOS-NYY
2	Ted Williams	196	70.1	275	3991	5142	1942	1954	23-35	1145	985	1374	275	35	1009	1134	132	341	14	1	3	99	12	6	.344	.490	.637	1.128	*7/H9	BOS
3	Ty Cobb	192	88.3	56	5274	6080	1908	1917	21-30	1405	1079	2000	327	164	913	605		374	55	130			629	113	.379	.448	.535	.984	*89/H743	DET
4	Lou Gehrig	187	87.8	357	5774	6985	1926	1935	23-32	1538	1385	1996	400	130	1489	1090		562	27	89			83	89	.346	.452	.645	1.097	*3/679	NYY
5	Mickey Mantle	186	80.0	362	4717	5860	1954	1963	22-31	1375	1120	1477	192	52	943	1094	89	971	11	9	31	56	115	18	.313	.441	.606	1.047	*8/H964	NYY
6	Rogers Hornsby	181	86.1	203	5291	6104	1918	1927	22-31	1387	1059	1948	350	120	1041	647		409	32	131			92	62	.368	.440	.595	1.035	*46/53H798	STL-NYG
7	Barry Bonds	175	84.3	346	5119	6391	1989	1998	24-33	1491	1096	1529	313	46	1051	1166	270	778	43	2	61	99	360	102	.299	.429	.581	1.009	*7/H8	PIT-SFG
8	Stan Musial	172	81.3	268	5897	6872	1944	1954	23-33	1525	1193	2031	425	121	1093	918	145	331	27	14	7	120	48	51	.344	.435	.594	1.028	9378/H1	STL
9	Shoeless Joe Jackson	170	61.5	53	4866	5566	1911	1920	23-32	1302	855	1737	305	163	775	510		219	59	128			198	81	.357	.424	.519	.944	798/3H	CLE-CHW
10	Jimmie Foxx	169	71.0	376	5380	6417	1928	1937	20-29	1464	1183	1794	304	87	1320	970		841	8	57			68	53	.333	.436	.632	1.068	*35/2H796	PHA-BOS
11	Tris Speaker	166	76.5	38	5290	6219	1910	1919	22-31	1438	967	1821	367	133	718	702		224	68	143			340	109	.344	.428	.485	.913	*8/H391	BOS-CLE
12	Albert Pujols	165	72.1	378	5539	6510	2004	2013	24-33	1483	1058	1756	386	8	1117	847	244	608	59	0	65	215	85	29	.317	.409	.594	1.003	*3D/H54	STL-LAA
13	Willie Mays	165	93.4	388	5880	6694	1955	1964	24-33	1542	1184	1852	297	93	1089	734	124	688	22	1	54	138	248	72	.315	.390	.595	.985	*8/H635	NYG-SFG
14	Willie McCovey	164	49.3	326	4493	5360	1962	1971	24-33	1372	775	1272	193	29	916	769	169	824	50	5	42	89	15	17	.283	.391	.557	.947	*37H/9	SFG
15	Frank Robinson	164	62.9	320	5266	6192	1959	1968	23-32	1466	1008	1605	321	43	1036	759	141	780	108	0	59	145	154	60	.305	.399	.564	.964	*973/H85	CIN-BAL
16	Hank Aaron	163	81.6	376	6004	6709	1957	1966	23-32	1536	1137	1914	316	52	1165	625	147	678	14	1	65	153	163	41	.319	.381	.577	.957	*98/4H53	MLN-ATL
17	Miguel Cabrera	161	55.7	330	5728	6606	2006	2015	23-32	1533	983	1872	397	10	1155	779	185	1043	43	1	55	201	32	16	.327	.408	.572	.980	*35/DH	FLA-DET

Albert Pujols and Miguel Cabrera are the only batters on that list to have actually signed a big contracts but their long contracts were at these ages:
Pujols 32-41 (OPS+ 112 ages 32-38 for Angels 2012-2018)
Cabrera 33-42 (Tigers 2016-2025)

The group above contains the players you'd expect. Note that Barry Bonds made the list for years 1989-1998, i.e., probably before he started using performance enhancing drugs (PED).

Babe Ruth's years start with his last of three as a full time pitcher: 1917. Ruth played no other position through 1917. It ends in 1926, one year before he broke the season home run record for the fourth and final time by hitting 60 in 1927. He then also led the league the next four seasons: 54, 46, 49, 46. Ruth should have gotten a 15 year contract.

Yankee catchers are tied with others at number 140 with OPS+ 129:
Bill Dickey 1931-1940; WAR 40.8
Yogi Berra 1949-1958; WAR 45.7

Among the 191, tops in WAR:

Rk	Player	OPS+	WAR/pos ▼	HR	AB	PA	From	To	Age	G	R	H	2B	3B	RBI	BB	IBB	SO	HBP	SH	SF	GDP	SB	CS	BA	OBP	SLG	OPS	Pos	Tm
1	Willie Mays	165	93.4	388	5880	6694	1955	1964	24-33	1542	1184	1852	297	93	1089	734	124	688	22	1	54	138	248	72	.315	.390	.595	.985	*8/H635	NYG-SFG
2	Ty Cobb	192	88.3	56	5274	6080	1908	1917	21-30	1405	1079	2000	327	164	913	605		374	55	130			629	113	.379	.448	.535	.984	*89/H743	DET
3	Lou Gehrig	187	87.8	357	5774	6985	1926	1935	23-32	1538	1385	1996	400	130	1489	1090		562	27	89			83	89	.346	.452	.645	1.097	*3/679	NYY
4	Babe Ruth	215	87.7	349	4181	5328	1917	1926	22-31	1236	1090	1471	296	86	1061	1065		693	29	51			85	79	.352	.486	.714	1.200	*79/183H	BOS-NYY
5	Rogers Hornsby	181	86.1	203	5291	6104	1918	1927	22-31	1387	1059	1948	350	120	1041	647		409	32	131			92	62	.368	.440	.595	1.035	*46/53H798	STL-NYG
6	Barry Bonds	175	84.3	346	5119	6391	1989	1998	24-33	1491	1096	1529	313	46	1051	1166	270	778	43	2	61	99	360	102	.299	.429	.581	1.009	*7/H8	PIT-SFG
7	Hank Aaron	163	81.6	376	6004	6709	1957	1966	23-32	1536	1137	1914	316	52	1165	625	147	678	14	1	65	153	163	41	.319	.381	.577	.957	*98/4H53	MLN-ATL
8	Stan Musial	172	81.3	268	5897	6872	1944	1954	23-33	1525	1193	2031	425	121	1093	918	145	331	27	14	7	120	48	51	.344	.435	.594	1.028	9378/H1	STL
9	Mickey Mantle	186	80.0	362	4717	5860	1954	1963	22-31	1375	1120	1477	192	52	943	1094	89	971	11	9	31	56	115	18	.313	.441	.606	1.047	*8/H964	NYY
10	Eddie Collins	155	78.1	20	5208	6386	1909	1918	22-31	1454	1008	1715	201	117	657	823		304	51	273			519	103	.329	.426	.424	.850	*4/6H	PHA-CHW
11	Tris Speaker	166	76.5	38	5290	6219	1910	1919	22-31	1438	967	1821	367	133	718	702		224	68	143			340	109	.344	.428	.485	.913	*8/H391	BOS-CLE
12	Mike Schmidt	155	76.5	370	5222	6355	1975	1984	25-34	1482	1008	1403	253	44	1009	1005	122	1254	47	12	69	92	136	71	.269	.387	.547	.934	*5/H634	PHI
13	Alex Rodriguez	146	76.2	423	5970	6889	1997	2006	21-30	1535	1198	1808	304	23	1203	752	58	1238	102	8	57	143	219	54	.303	.387	.574	.961	*65/DH	SEA-TEX-NYY
14	Albert Pujols	165	72.1	378	5539	6510	2004	2013	24-33	1483	1058	1756	386	8	1117	847	244	608	59	0	65	215	85	29	.317	.409	.594	1.003	*3D/H54	STL-LAA
15	Jimmie Foxx	169	71.0	376	5380	6417	1928	1937	20-29	1464	1183	1794	304	87	1320	970		841	8	57			68	53	.333	.436	.632	1.068	*35/2H796	PHA-BOS
16	Mel Ott	161	70.4	323	5490	6559	1929	1938	20-29	1498	1148	1730	301	54	1206	969		462	35	60		44	54		.315	.421	.566	.987	*958/H4	NYG
17	Ted Williams	196	70.1	275	3991	5142	1942	1954	23-35	1145	985	1374	275	35	1009	1134	132	341	14	1	3	99	12	6	.344	.490	.637	1.128	*7/H9	BOS
18	Rickey Henderson	141	70.1	168	5118	6163	1982	1991	23-32	1387	1146	1478	258	37	565	976	29	708	35	6	28	87	805	170	.289	.404	.452	.856	*78/DH	NYY-OAK

It does not include Ruth's pitching WAR in 1917, 1918, 1919. Number of players in these WAR ranges:
90s: 1
80s: 8
70s: 9
60s: 10
50s: 38
40s: 53
30s: 47
20s: 26
Jeff Burroughs 117; OPS+ 125
Matt Kemp 16.8; OPS+ 125

Finally, most home runs and remember Ruth was still pitching and Bonds was still clean:

Rk	Player	OPS+	WAR/pos	HR ▼	AB	PA	From	To	Age	G	R	H	2B	3B	RBI	BB	IBB	SO	HBP	SH	SF	GDP	SB	CS	BA	OBP	SLG	OPS	Pos	Tm
1	Alex Rodriguez	146	76.2	423	5970	6889	1997	2006	21-30	1535	1198	1808	304	23	1203	752	58	1238	102	8	57	143	219	54	.303	.387	.574	.961	*65/DH	SEA-TEX-NYY
2	Sammy Sosa	139	49.0	421	5439	6104	1992	2001	23-32	1398	955	1560	234	30	1123	577	112	1395	34	5	49	118	179	78	.287	.356	.573	.929	*98/H	CHC
3	Ken Griffey Jr.	150	62.6	400	5116	5931	1992	2001	22-31	1355	992	1509	269	27	1094	707	152	927	55	2	51	98	125	40	.295	.383	.593	.976	*8/DH379	SEA-CIN
4	Willie Mays	165	93.4	388	5880	6694	1955	1964	24-33	1542	1184	1852	297	93	1089	734	124	688	22	1	54	138	248	72	.315	.390	.595	.985	*8/H635	NYG-SFG
5	Manny Ramirez	160	51.3	385	5299	6263	1996	2005	24-33	1437	1038	1686	362	14	1242	835	128	1157	72	0	57	157	24	22	.318	.414	.610	1.024	97D/H	CLE-BOS
6	Albert Pujols	165	72.1	378	5539	6510	2004	2013	24-33	1483	1058	1756	386	8	1117	847	244	608	59	0	65	215	85	29	.317	.409	.594	1.003	*3D/H54	STL-LAA
7	Hank Aaron	163	81.6	376	6004	6709	1957	1966	23-32	1536	1137	1914	316	52	1165	625	147	678	14	1	65	153	163	41	.319	.381	.577	.957	*98/4H53	MLN-ATL
8	Jimmie Foxx	169	71.0	376	5380	6417	1928	1937	20-29	1464	1183	1794	304	87	1320	970		841	8	57			68	53	.333	.436	.632	1.068	*35/2H796	PHA-BOS
9	Jim Thome	156	51.1	371	4849	5994	1994	2003	23-32	1422	985	1396	271	20	1015	1064	93	1473	39	1	41	81	13	15	.288	.417	.582	.999	*35D/H	CLE-PHI
10	Mike Schmidt	155	76.5	370	5222	6355	1975	1984	25-34	1482	1008	1403	253	44	1009	1005	122	1254	47	12	69	92	136	71	.269	.387	.547	.934	*5/H634	PHI
11	Jeff Bagwell	156	61.0	366	5450	6673	1994	2003	26-35	1495	1160	1643	358	16	1155	1066	124	1120	91	0	66	158	166	60	.301	.420	.574	.994	*3/HD9	HOU
12	Juan Gonzalez	138	33.7	365	5129	5616	1992	2001	22-31	1312	862	1548	302	20	1161	367	64	972	49	0	71	144	19	12	.302	.350	.582	.932	9D78/H	TEX-DET-CLE
13	Mickey Mantle	186	80.0	362	4717	5860	1954	1963	22-31	1375	1120	1477	192	52	943	1094	89	971	11	9	31	56	115	18	.313	.441	.606	1.047	*8/H964	NYY
14	Lou Gehrig	187	87.8	357	5774	6985	1926	1935	23-32	1538	1385	1996	400	130	1489	1090		562	27	89			83	89	.346	.452	.645	1.097	*3/679	NYY
15	Carlos Delgado	146	40.9	357	5307	6374	1996	2005	24-33	1485	946	1527	379	14	1138	867	144	1291	136	0	64	103	8	6	.288	.397	.566	.963	*3D/H	TOR-FLA
16	Babe Ruth	215	87.7	349	4181	5328	1917	1926	22-31	1236	1090	1471	296	86	1061	1065		693	29	51			85	79	.352	.486	.714	1.200	*79/183H	BOS-NYY
17	Barry Bonds	175	84.3	346	5119	6391	1989	1998	24-33	1491	1096	1529	313	46	1051	1166	270	778	43	2	61	99	360	102	.299	.429	.581	1.009	*7/H8	PIT-SFG

Mantle, Mays, Aaron: they look like they would have been very good candidates for ten year contracts, Mantle pretty much exactly. The Mick had only one more star season: 1964. Mays and Aaron several more. If you're timid about signing current young arbitration eligible and/or free agents for ten years, consider whether you would have missed the boat on Mantle, Mays, Aaron and others.