well, just wait, any CPU upgrade isn't really worth it, the Q6600 still one of the fastest 775 CPU (the fastest stock is the QX9770 3.2Ghz) and you're really lucky if you can find one, and you still need to pay a great amount to get one, an I3 or a FX-6300 would be cheaper (and new) and faster...
I know you don't want to OC but i would give a 3ghz shot (it's really easy, dial 333mhz FSB and many will work with stock Vcore, if that doesn't boot, try 1.3Vcore, it should be enough)