I just got a x800 gto agp for $155 newegg. I managed to unlock the pipes to 16 equaling 6800gt and oc to 425/1050 stable. If you get a better cooler you could probably hit 450/1200. Also download the omega drivers and use built in ati tools to control fan speeds and let it find max oc if you do buy card. I am very happy with it seems to be better or equal to the 6800gs/6800gt cards.
Im running my card with a p4 3.06ghz 800mhz fsb 1gb pc3200 ram and a msi mobo and my fps in all games on medium to high settings gets me 40, 50 + fps.
Oh also if you get card and want to know how to unlock card pm me and I will send you correct bios and tell you how to flash card.
i3 540 @ 3066 MHZ
4GB DDR3 1600 1T 9-9-9-28
HD 5750 @ 850/2400
Antec Lanboy Air