Why does my CPU throttle, when it's not because of the CPU temp!?

[mikkelmk]

I was really looking forward to get the Xigmatek Dark Knight CPU cooler for my new self-build PC, so i could overclock my Q9550, and i got the cooler some weeks ago. But when i overclock (2,8 GHz to 3,4 GHz), it throttles, and i can't find any damn explanation? I've searched the web, asked in a lot of forums, disabled C1E and EIST and tried a lot of different settings. But when i run Intel Burn Test or Prime 95, it throttles. There are no errors in Prime95, Intel Burn Test says it's stable, it just goes quietly from a multiplier of 8.5 to 6.0 in one second. And the weird thing is that when it throttles, it's still under full load! And you probably think it's because of the CPU temp, but RealTemp, CoreTemp and Speedfan says it's around 60C under full load (it drops like 2-5 degrees when throttled).

WHY? Can anyone tell me why it throttles when it's not because of the CPU temp?

Specs are:
CPU: Intel Core 2 Quad Q9550
Motherboard: Asus P5Q SE
RAM: Corsair XMS2 2x2GB DDR2-1066
PSU: Corsair TX650W

BIOS settings are:
FSB: 400
PCI-E: 100
DRAM frequency: Have tried on 800 Mhz and Auto

Vcore: Have tried 1.15 to 1.25 and Auto
DRAM voltage: Have tried 2.1 and Auto

CPU Spread Spectrum: Have tried Enabled and Disabled
PCI-E Spread Spectrum: Have tried Enabled and Disabled

C1E: Have tried Enabled and Disabled
EIST: Have tried Enabled and Disabled

Bios is updated.

It sucks to know you spend money on a new CPU cooler and then get to know that you can't really use it, but it sucks even more if you don't have any f--cking idea why. I'll really be happy if i could find out

PS: Please don't tell to read some guide, i've read A LOT of them.

 

[doakwolf]

Perhaps try a little more voltage @ the CPU core? It should be safe to about 1.35v I believe. Can't hurt as a troubleshooting method?

 

[mikkelmk]

Now i've tried with a vcore on 1.3, but now it throttles almost immediately, before it took some minutes to throttle, so i don't think it's because of the vcore.

Could it be the north brigde temp? :S