Quad to dual... What kind of temperature drop should I expect?

Hi,

I have a matx form factor computer. Right now I have a Q6600 (GO step, TDP 95W, 65nm) inside it, and it runs around 42 at idle and 63 on torture at 2.4GHZ stock.

This particular machine doesn't require a Quad though, and would make a better use of a higher clock cpu. Now, I assume from research that if I replace the Q6600 with a dual core, let's say a E7400 (TDP 65W, 45nm), and keep the exact same cooling setup, the temperature should drop a bit, even if stock speed is a bit higher at 2.8GHZ.

What kind of temperature drop should I expect? Is there a chart or data out there on how hot cpus are actually running at stock in a given system? I'm looking to slightly overclock it from 2.8ghz to 3.2 or 3.4ghz, but I wonder if I'll be able to do it without changing anything to the actual cooling.

Maybe someone did the opposite, going from a dual to a quad in the same system/cooling, and can tell how much the temperature rise from his experience.

Thxs.