Massive G (from Chad's board) told a story about him seeing Vic get weighed right in front of him, and he weighed something like 290 and was damn near contest ready (IIRC).
No matter what anyone says, Vic had an unreal physique and the genetics to respond to all of the "supps" without looking like a bloated mess.
I know he didn't compete in any large competition, and that causes many people to question what he would have looked like had he dieted down. No matter what one's argument is, Vic was holding onto and maintaining a 300 lb. physique long before anyone else was close to that mark in that condition.
I have heard stories that Ray Mentzer (who hated competing) had been up to a relatively lean 290 at one point, but his health may have suffered from getting that large, as his kidneys ultimately failed.