I'd be more comfortable putting my money on the absolute best version of Ray. Great chin, very good jab, and heavy hands. I think Cooney would fold in the later rounds of a competitive fight.
If it was 15 rounds, I'd back Mercer all the way. 12? Probably Mercer but Cooney might just do enough damage to sneak a decision, I think Cooney had a bit more to his game than Morrison.
The version of Cooney that fought Holmes would be too much for any version of Ray Mercer. Even Larry had to be cautious in there with Gerry. He was like a bomb squad soldier taking his time with precision and patience. I don't think Ray can box good enough to keep Cooney off him. Mercer did have the best chin but with Cooney I think Ray may absorb them and survive. He would be shook though, stopped in his tracks. Cooney TKO mid or maybe a decision win.