Well, let's see if you can gain something from my experiences below:
System1: 3600x2, 3.1GHz, Evga NF59-SLI, Antec Trio 550, G.Skill ddr2-800, Zalman 9500A, Seagate ST380011A, 8800GT 256mb, winXP
System2: 3600x2, 2.9GHz, Gigabyte M61P-S3, Antec Earthwatts 430, G.Skill ddr2-800, Zalman 9500A, Seagate ST380011A, 8800GT 256mb, winXP
Two same CPU, same RAms, OC'd using same mult/divider. Look closely at the supporting cast. I tried Earthwatts on system1, passed Prime95 but choked on 3dm06 at 3.1GHz as expected. M61p didn't go past beyond 2.9G stable even with Trio psu b/c of mobo limitations (somewhat limited memory tweaks).
I think you hit the max. If you want extreme, find a mobo that can give you Vcore more than 1.4V. Three things: Stabilize your CPU first with 1.5v, grab a good PSU, then play with fsb and mem freq/volts/drive settings. Two unknowns enough to drive you crazy.