How much are you willing to pay? Are you planning on buying a PC or building a PC? I suggest you build one, it's cheaper, and you can make it exactly how you want it. And no, you don't want the fastest CPU there is, because both intel and AMD's fastest CPU is $900+. The fastest budget high-end CPU would have to be the 3700+ San Diego, it sells for about $340.
so, umm, err yeah