Please check this spec!

[KIA]

I'd like to O/C the 8400 to 3.6GHz. I already have a water cooling system & case from previous build.

Cheers.

 

[semi-pro waster]

All looks good to me, the parts are compatible so as long as your watercooling fits socket 775 chips it should be fine.

 

[decto]

The e8400 should hit 3.6Ghz on the stock cooler.

With water cooling you should be able to push it a lot harder or you could consider a Quad G0 which should hit 3.6 on water.

AD