I'm buying a new monitor (22" 2232BW Samsung). Its native resolution is 1680X1050. I've a pretty lame graphic card (Asus 8600GT 512MB DDR2

). And I love to play COD4. Basically I want to upgrade, because I an madly in love with the GTA series, and have my finger crossed for the PC version to come out. And I don't want to miss the tiniest details of the game. 8600GT Works fine with my current resolution. But I highly doubt if it'll work the way it is at my current resolution.
So, I want to buy a graphic card (don't have much budget for it, since I'll also be buying a new 650 Watts PSU, to go with the graphic card, I'm currently using PSU that came with my Desi 2000 Rs. Casing :P). Please suggest me a good 600+Watts PSU (crossfire/SLi Ready), it should be compatible with the graphic cards like 4850, 4870 and GTX 260...
The 4850 is available for 15k, whereas 4870 is available for 25k. I would like to buy the 4870, because I feel it's a semi-future proof card. But will a 4870 be an overkill for a 1680x1050 resolution?
Whichever card I buy, I want to be sure that it'll play most of the titles at maximum details and quality + eye candy. Maximum Support AA and AF!