See my sig. The only thing holding me back from going any further is my ATI AIW 9600 Pro card. It doesn't care much for anything over 72mhz AGP. Darn shame to. I've had my chip upto 2.2ghz with stock cooler and voltage, but AGP craps out.
Check that thread...several guys over 3000MHz with Volt mods on a Shuttle AN50R's. With NForce 3-150 chipsets, many are 2500MHz or more with little or no mods.