How much can i oc my q6600

theAnimal is right. Also, it depends on what else is supporting your system--power supply, RAM, it all plays an important part in your OC. Bottom line remains that you don't know until you start OC'ing. My 6600 can take a quick sprint to 3.2 with no additional voltage, my wife's 6600 doesn't like to hit 3.0 without more voltage--identical chips, but vastly different to OC.
 
We don't need ... you do.

With a late model G0 core, you should be able to reach 3.0 GHz at stock voltages and a good cooler. 3.3 GHz shouldn't be hard. Anything more will depend on practically everything in your system except the video card and hard drive.

Mine runs at 3.6 GHz. (Prime95 stable for 72 hours; core temps 61 - 65 C). Hey, I went away for a weekend and just let it run.

HOWTO: Overclock C2Q (Quads) and C2D (Duals) - Guide v1.6.1
http://www.tomshardware.com/forum/240001-29-howto-overclock-quads-duals-guide

Core 2 Quad and Duo Temperature Guide
http://www.tomshardware.com/forum/221745-29-core-quad-temperature-guide

You also should have something about your specific motherboard.
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Overclocking since 1978 - Z80 (TRS-80) from 1.77 MHz to 2.01 MHz
 
I get my Q6600 to 3.6GHz aswell works wonderfull.
Multiplier x8.0
Bus speed 400MHz
FSB 1800MHz

The only problem i get is that i cant run my 4x1GB ddr2 in 1066 so i run them in 900
 
I have a buddy of mine who could oc to 3.5ghz on the q6600 G0 stepping.. But he has a lousy mobo which limits his oc.. That said most people might have awesome chips or lousy ones like mine.. At such high voltages I could only get my e8400 @ 3.8ghz..
 
the only problems whit 3.6GHz+ is the Heat. its get very hot on loads. so whit more advance cooling like water. having the q6600 on 3.8GHz and up is not a problem. but i think the cap on a normal air cooled cpu. is at 3.600mhz
 



8 x 400 = 3.2 not 3.6

400bus quad pumped is 1600FSB not 1800.

Retard!