Currently have an ancient 7800gt with an e8500 at 4ghz. Cs source is running fine, but l4d is struggling with this gfx card so i want to upgrade, say my budget is £150 ish, can do more but want it to be worth it, what would you recommend, i was thinking a 2nd hand 4850 for £80 ish but ATI cards have issues with source, so i am swinging towards a GTX 260, needs to fit in a silverstone sugo1 case, and i play on 1440x900.