Hi there. I know this cpu isn't last news but i have tried a bit more overclock on it, and in order to get 4ghz stable i need to set 21x190 or 20x200 with 1.35v vcore, and everything else set to auto.
Problem is that i get terrible temperatures at 4ghz, with prime95 running i get 88ºC to 91ºC. I got a nice Cooler Master V8 and artic silver as thermal compound, and i have checked and rechecked the cooler assembly work on the board and everything is fine. I've tried other different thermal compounds and other heatsinks and results are always similar from the beginning.
Other than that the system runs perfectly stable but i'm not willing to risk the cpu, and at 3.6ghz with 1.25v vcore i get 75ºC maximum temp running prime95 and 47ºC at idle.
That said, could i go ahead and figure that it's the cpus fault? I remember reading a long ago that not all i5 750 aren't the same and some people got more lucky than other!