I don't care what people say, you need 1.40-1.42v to run the Q6600 completely stable. Prime 95 is overkill, but for a short time 30 minutes or less will give you some insight into stability.

When you guys post your vcore, make sure it's CPU-Z or some other program other than your bios setting. My MSI undervolts significantly from what the bios says the CPU is running at.

I would say that anything over 75C for long periods is not a good idea. The Intel stock cooler idles in the 50's.

I can run my quad core at 1.225v all day at 3.2GHz but it could crash at any time and has, but is quite stable. Getting to 3.6Ghz takes 1.4v

My opinions are only for air cooling, not water cooling, but I think it may be similar. Water cooling just allows 4.0Ghz or more with 1.5v +