Heh well you can forget 4ghz on stock cooling. In fact, with stock cooling your OCing options are very limited. IMO, at most if you have 1600mhz RAM, set your Base Clock to 160 and set the RAM timings to their ratings and leave everything else on auto and see what kind of temps you're getting.
If you decide to upgrade you cooler (an absolute must for OCing) then some rough voltage settings you might use are:
175 base clock, turbo on
200 base clock, turbo off, EIST off, 20x multiplier
LLC on. If you have Vdroop, you'll need more Vcore (for both these settings)
Anyway, OCing all comes down to the user doing it. How much can you get? Mobos and CPUs have their own quirks. Some are better than others. The point is, try it for yourself after reading some how-tos. Just make a small jump, test it... if everything seems ok, increase it a bit more. OCing should be a fun or at least interesting process. It's not like setting some default values (ie: for this, input this. For that, input that).
Also, Tom's did an i5 750 review on OCing and efficiency you should check out. Goes into some detail and also has voltages posted so there will be some good info for you there. (Oh, that's what matto17secs linked )
The best budget cooler is the Hyper 212+. It performs like some coolers twice as expensive. If you want a really good one, Megahalems or Noctua make some really high quality ones but they're pricy. I have a Zalman CNPS10X Extreme which is very good, very quiet. There's some other cheaper Zalman coolers that are fairly good as well. Depends where you want to get it from, but IMO maybe just check out either a local retailer online or newegg if that's what you like, and pick one for 1156 socket compatibility based on price... maybe select 3 or 4 you like and then just check out some reviews. You can go to frostytech.com or silentpcreview.com, among others.
MMM... Although the Hyper 212+ is good. I actually perfer the new CM releases. The V6 is also very nice, with the dual fan config at the same price as the Hyper 212+ i find it to be a great deal, however they don't exactly have reviews out for it, they have it for its counter part though the V6 GT, but thats 20$ more, it's possible to see relative performance though.