When the two men were in their primes, I would always go with Holmes, but in the 1990's and in their comeback versions, I think it could go either way... I'm not convinced that this is a cake walk for Larry, regardless of how well he looked against Mercer and how poorly Foreman looked against Schultz or Morrison.. This was not the wild swinging Foreman of the 70's, who left himself wide open and tired in the mid rounds. His jabs were straiter, defense tighter, and was patient at looking for the right opportunities rather than wasting punches... I think he also took some notes after losing to Ali and Young. In addition, Holmes would always be prone to getting tagged with a sharp right hand to the left side of his face, and Mercer had him realing in the first round of their fight ( though I don't recall which punch caused it. ) Again, its reasonable to pick Holmes via decision had they fought around 1992, but I'd have less confidence in Larry taking the battle of the ages when both were past it...
It's interesting to note that few seem to think that a 1992 Holmes can go the 12-round distance with a 1973 Foreman, yet Gregorio Peralta took Foreman 10 rounds once and into the tenth another time. I assume most people think Foreman improved a lot between 1971 and 1973; this improvement must be in terms of skill, because Foreman way almost always in the 215-225 range in his first career.
Any version of Foreman has a tough time with most versions of Holmes you mentioned although I think young George outpoints old Holmes.