I've seen a few people suggest using over 1.4 volts for vCore. After some initial issues, most OC'ers seemed to come to a consensus that 1.365v was considered to be the maximum acceptable voltage for the 45nm CPUs. I'm just throwing that out there for you, so that you can take that into account.
Also take into account that even with that vCore limit, the E8400s usually don't need all that much voltage to get stable OCs. That said, mine needed 1.275 to run 3.6, so it's quite possible that you do need another bump of vCore - you just might want to lower the max limit you'll consider to 1.365v. It seems that with decent cooling, most people run into the voltage limit, before temps become an issue.
I've seen a lot of nice OCs at lower volts than mine can manage, but just for your refference, here is the overclock data for mine, including all voltages required for stability at the various clock speeds.
Or if you are only interested in 3.6GHz, in my case (C0 E8400) I set 400*9, vCore 1.275 (BIOS set) underclocked RAM 4-4-4-12 @ 800MHz DDR2 @ 2.1v CPU VTT: 1.30v, MCH1.25 @ 1.40V (uGuru shows 1.45). Tuniq @ 1740RPM CPU peak temp 48C (47 AVG) 35C idle. uGuru temps: CPU 43 System 26C, PWMs 41/42/43/41/39
SuperPi1M:12.750sEdited by 8KCABrett - 12/28/08 at 8:02pm