justbb, you always ask the hard questions...good ones but hard.
While I think the travel at the MLB does make life easier, I know playing 40 straight games affected our son. Certainly he was not as strong or mature as Ripken, not to mention the mental strength. His manager suggested the inability to get a day off affected him and his performance. At one point he got his average to .330. By the end of the 40 games he was down to .310. At the time he insisted he still felt good. One month later admitted he was really hurting. My impression is it affects performance, but the timing might be unpredictable.