|1st of all, where does it say you were going to overclock to 4.0GHz?|
2nd, how much overclocking experience do you have? I've been building computers for over 15 yrs & have been overclocking since the days of the Pentium 1.
3rd, while admittedly I have no experience with the Core-i series, I have regularly overclocked other CPUs, both AMD & Intel, as much as 25-40% (depending on CPU/board combo) using stock cooling. I've never had any problems.
BTW, how the hell can anyone tell you whether a HSF is going to fit in your case or not? Especially since we have no idea of which case you have? Anyone with a brain should be able to tell when they run out of characters in the subject line, don't you think?