Guys like Bane and Croc and Grundy should be played by naturally BIG guys. They can't just be really bulky 6-footers standing on apple boxes - they've got to be big *and tall*, like that Singh guy. They've got to positively *tower* over Batman, more than even Ra's did in Begins. 7 feet plus would be ideal.
Bane should always be big and not get any larger when he's on the venom. You can't just have mass coming from nowhere, Hulk style, it's silly. Venom should just be like super-adrenaline or something.
You'd probably need another actor doing the voice, because the combination of huge guy and decent actor (who can do the right accent) is unlikely. But you *don't* need to have him always masked to do that - you can dub one actor with another's voice and make it look perfectly fine. Darth Maul's voice was done by a different actor than Ray Park, and Andy Macdowell was completely overdubbed by Glen Close in one of her films.