If it's a pure gaming PC, duo's outperform quads in most current games due to the higher clock speed. Grab a E8400 or E8500 and save yourself a couple hundred dollars, they'll clock to 4.0 GHZ easily. Now you can probably put the Rampage in the budget. And some LN2.
Wish I had 5k to blow on a computer. Good luck with your build
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Intel E8400 Biostar Tpower I45 Diamond HD4870 512mb G-Skill DDR2-1000 4GB Creative Xtreme Audio PC P&C 750W Quad Silencer Antec 900 Logitech G-15, G-5
WC Loop: Swiftech Apogee GTZ Danger Den CPX-Pro, Maze 4 GPU Black Ice GT Stealth 240 Rad