at that resolution 5750 will allow you to game on max settings and 500w psu should be enough for it but you should mention your psu make and model btw if you are asking about 5750 why do you mention gtx460 prices(those prices are absurd tho gtx460 can be had for around 10k these days) and 6850 ?
460 is tooooooooooooooo much for that resolution. get a HD5670 512MB @ 4.5k
whats your budget for GPU? you intend to hold on to your monitor for how long? no point buying a GPU for a low resolution monitor if you end up buying a bigger one in some months