Athlon mobile 2600+ (cos mobiles aren't multiplier locked) running at 2.3Ghz (3200++) with a 405MHz FSB, with room to move later
It has a thermalright SLK900A (Huge Copper biatch) with Arctic Silver 5.
Default voltage, multiplier dropped to 11, FSB increased from 266 to 400Mhz for maximum throughput.
1 large 120mm Sunon 120CFM fan sucking air out the back, two small 80mm rifle bearing (quiet) fans blowing air across the (4) HD's. 1 fan blowing air across the video card.
Video card set to standard speed, don't need any more heat, and performance difference will be minimal.