It wouldn't take that much to make a xbox 360 beating pc. nvidia gefore 7600gt's are going on ebay for 30 quid, you can run those in sli, get a asus sli deluxe motherboard. bit of ram. Amd 64 fx 53 was going on ebay the other day for 30 pounds. I mean sure if you want everything top level, its going to cost, but its not going to take top level to beat the 360 or ps3.
Plus with the xbox i always found that the best games you wanted to play usually were out for pc anyway and fps games work better with a mouse in my opinion.
I play warrock also, and bigbud, you misunderstand the ratio in the game, for every time you get killed you are killing 1.96 ppl on average.