"Messing" with AA has to be done if you want to max a game.
Two 460's have a bit more power than a 480, but, if I remember, the 580 is faster than the 480 by a fair amount.
What I'm trying to say is, the term; "maxing", is very open to debate. The way I see it, maxing a game is cranking up everything to the max, AA at full, AF, DOF, PhysX, Tesselation, the whole lot.
Sure, you could turn AA down from 32x to 4x in most games without really noticing that much difference, and the framerate would increase, but, in my eyes at least, that's not "maxing" a game.
With a 580, you could run Metro at high settings and get decent framerates, but you certainly won't be able to crank it to the max on everything and get anywhere close to a playable framerate.
Then again, "playable framerate", also differs depending on what the user considers it to be.