Alrighty, time for my 2 cents. I run an i7 2600k at 4.5Ghz with Hyper 212+ and my temps max at 81C on 18 hour P95 blend. Some CPUs run a bit cooler than others, some require more voltage. There's no way for anyone to tell someone what they would need to accomplish a certain OC. Of course if you're going for higher clock, you want to be on water. If you're just looking for settling in the 4.5Ghz range, you still may need watercooling to keep your temps lower and increase cpu life.
It sounds to me like the OP wants to push his OC as high as it will go, and still be safe. You should probably go watercooling for that. If you plan on finding a good overclock with 1.4v being your personal voltage limit, you're probably going to want watercooling for that. It's a greater chance that your chip will run pretty hot at 1.4v. If you're willing to spend the extra cash, get watercooling. My advice to you, get watercooling. And oh ya, get watercooling.
And I'm not a big fan of someone jumping on a thread and claiming that "oh, 4.5ghz on blah blah cooler, thats easy!" Just because it was easy for you doesn't mean it's easy for everyone else. Maybe you're lucky, maybe your just smarter than most of us, I dunno. What I do know is, this sort of statement encourages OCers with less experience to take higher risks than they probably should. Bad joo joo imo.
As for the statistics regarding the percentage of sandy bridges capable of doing certain clocks, that information is old and outdated. Those were the initial estimates posted by someone at Intel, but that same poster later admitted that it's likely that these chips can do better than that. I'm almost certain they came to those figures using D1, and D2 changed the ballgame. In the end, it doesn't matter what percentage of chips do what, it only matters what your chip does.
I cannot stress this enough. You pick your safe temp limits. You pick your safe voltage limits. If you fry your processor, it's on you. Not anyone else. As someone else mentioned before, OCing (especially on newer chips like sandy bridge) is a lot of guess work. Nobody knows what is going to make your chip last 3 years or more. If you want your Sandy to last that long, your best bet is to simply not OC it. Period. In 2 more years, we will have a better idea of the do's and dont's to making your CPU last 3 years.
Sorry for the long post, just had to get this off my chest. Good luck and enjoy your new build!