See supporting data.
The 15 seasons 1954-1968 cover both players peaks. In 1969 Mays started to decline, probably because he was three years older, although Aaron inexplicably perked up at age 37 in 1971, three years later. Curious. Or suspicious.
OPS+ 157 (career 155), OPS on road against the other teams .97054387704517.
OPS+ 163 (career 155), OPS on road against the other teams .97908857970998
OPS+ home and road against all teams 1954-1968: Mays 3.77% higher
OPS on road against the other teams: Mays .88% higher
If my method is accurate, Mays and Aaron may have been closer than OPS+ would suggest. See previous posts on this with Ted Williams v. Joe DiMaggio ten seasons (1939-1942, 1946-1951) and Ted Williams v.Mickey Mantle seven seasons (1954-1960).
With my method:
Williams 6.39% higher than DiMaggio
Williams 11.16% higher than Mantle