Who would've won I think Miller would've beat Martin that AJ fought. I'm just not sure Klitschko (that fought AJ vs Miller?
Wlad would have boxed his head off, even at 41 he was twice as quick as Miller and J hit Wlad harder than Miller would, it would just be a question of whether Wlad`s older legs had the stamina to keep up with the pace that Miller would set with his high volume punching.
Wlad would of out boxed him before eventually landing a bomb and KOing Miller. Miller is just too easy to hit, his pressure might cause Wlad some problems but we know Wlad deals with that by clinching and while Miller is 300lbs, Wlad was very adept at leaning on guys. You might be 300lbs but that doesn't mean your neck can take a 240lbs man pressing down on it. Where your head goes your body follows and an adept clincher knows how to control an opponent through technique not just size and strength. Remember how Lewis mauled the bigger Grant on the inside pushing him down into that uppercut? Wlad was trained by the same guy, learned the same techniques, doesn't matter how big Miller is your only as strong as your weakest point when an opponent knows how to use find and exploit that weak point.