Dude I own "75" cards. 768mb is NOT any good for playing games at that resolution. 19x12. Especially if you're playing in DX10/11. Those weigh heavier than DX9.
and you think the 1gb variant would do well in dx11 @ that resolution? no no buddy.
i dunno about you folks here but i bought my gtx460 with the full knowledge, it being a first gen dx-x (where x is series number) card that it'll struggle with it, the same way the riva tnt, fx5700ultra, and my 9600gt (which cost the same as my 768mb when i bought it) struggled. i can only vouch for mainstream cards though.
gtx460s (both variants) are also very very overclockable, mines running @ 850/1700 with a minor volt bump.