be aware that when people say "higher resolution" that would be 2560x1600, where the 768mb chokes due to lack of frame buffer. if you're not going to play @ that resolution (i assume so, that's why you're looking @ the 460, since that resolution is mostly reserved for higher end systems), an overclocked 460 192 would do you good.
the only catch is that a properly tweaked (overvolted/overclocked) 460-256 can go berserk and reach gtx470 levels, but leave that to the non-reference pricier models.
i have my 460 192 bit running @ 800/1600/1825, and it's doing good.