Problem with overclocking E5200 with asus p5ql pro

I am a first time overclocker and will use my new desktop with Photoshop and film editing.

mobo : asus p5ql-pro
proc : e5200
memory : geil ddr2 800 4G match pairs
display : sapphire hd4670 ddr4 512mb
psu : cooler master xp550

I read many successful attempts with the e5200 but I can only manage to oc my e5200 to 3.2 ghz with 12.5 x 256 fsb stable at stock voltage. I can not tune up the 'vcore' because I did not find any adjustment on this mobo. I've got two questions:

1. I have tuned the PCIE frequency to 100 as instructed by oc articles I read, could I use higher frequencies or would it be better if I reverb the frequency to auto now?

2. Any way out to tune up the 'vcore' with my mobo as I do want to test the headroom of my e5200?

Any assistance will be appreciated.

Mike

Thanks a lot. I found the cpu voltage which is in a hidden manual and tune the 'vcore' to 1.22v. Now I can run my system stable at 266 x 12.5. The cpu temp reads 54c when I run Prime95, is this acceptable?

Many thanks.