No need for 4000+. You can always go in for 3000+ venice + Asus A8n-E SLI+2*512 MB Twinmos Ram+the graphics card. Overclock 3000+ to 2.2~2.4GHZ. You wont be finding any problem with this. But do make sure you buy a good PSU like those from antec with 500watts or else u will have tough time in overclocking your proccy and also the 7800GT is power hungry. So apart from proccy keep your eye on the Ram( I reccommend you twinmos), Power safe, and the cabbinet.