Is it intel or amd? And which one is it?
Your answer has many many determinants like what type of cooling you're using, air or water. The volts on the cpu applied. Ambient temp where the pc is running. I can go on but your question is left wide open.
Phenon II would probabily be the coolest
If I do oc I usually don't hit it hard. Maybe like from a 2.6 to a 2.8 or 3 just for fun so not much added volts to the cpu. Air cooling is all I need. The ambient temp is around 74. I am not a gamer but do a lot of video editing.
I have a amd phenom 9500 quad core and it runs at like 40c doing nothing and up to 50c when playin games
Wow, my Q6600 is around 30 idle and 40-42 maxed out.
My Q6600 OC'd to 2.7 from 2.4 only hits 43*C when under 100% load (Video conversion).
It's about 27-31 Idle.
What cooler are you using and how fast are you running the fan?
I'm using the cooler that came with my PC when I originally bought it (I bought it as an acer about 9 months ago, then gutted it). The fan speed is set to automatic.