This is my first overclock, and here's where I'm at right now:

Q6600 (G0) at 3.2 GHz (9x356)
Memory at 5-5-5-18

With cpu voltage at 1.2375v (bios), Prime95 25.4 ran Small FFTs for 4 hours before an error. Now I've got it running at 1.25v (bios), but it's only been running for 1 hour so far. I'm guessing that I'll end up at 1.25v or 1.2625v (going for 12 hours of prime95). Temperatures at 1.25v with prime95 running Small FFTs give 48/46/46/48 for my 4 cores (using coretemp).

1) Is 12 hours of prime 95 Small FFTs a good enough test to determine whether or not the overclock is stable?

2) When I attempt to reduce the memory timings, will I want to switch to a different test in prime95 that stresses the memory more?

3) At what point will I notice diminishing returns for real-world applications like gaming FPS? Would it be worth it to try 3.6 GHz?

4) Will running at 3.2 GHz 24/7 shorten the life of my processor?

1) Yes, 12hours is fine if you're not going to use your pc for 12hours straight.

2) Yes, that's the blend test. 8hours minimum, more recommended.

3) Depending on what applications and games, the gains are decent, but not necessary.

4) Yes, but as long as the core temps are under 65C and the voltage under 1.5v, you should expect at least 2years, if not 3.