upgrade from x1800xt 512mb... advice needed

[G1BB0]

looking to do a minor upgrade in next couple of weeks and cant for the life of me decide which card is best suited.

pc spec - c2d 4300 (running at 3ghz per core )
2x OCZ XTC Platinum OCZ2P800512 (1gb total, gonna buy another 2gb aswell)
Asus p5n-e sli
dell 2005fpw
corsair 520watt psu

mainly playing cod4 at the mo and just want a bit more eye candy/fps

main cards I am looking at are the 3850 and 3870's

what sort of performance boost would they give? budget about £150 - 200 absolute max

 

[willhub]

Wait untill the end of jan, 3870X2 will come out and push down the price of the 8800GTS 512 into your budget.

 

[G1BB0]

its gonna be around that time anyway, what boost would the gts give over the x1800?

 

[willhub]

its gonna be around that time anyway, what boost would the gts give over the x1800?

8800GTS 512mb? I should think a massive performance boost . COD4 will fly on it at 1680x1050 res aswell.