Guys dont forget he's asking about increasing the speed to 3.2ghz, not 4ghz. 3.2 can be achieved with barely any voltage increase at all. I'm not against after market coolers but he's asking if its worth buying a new cooler to jump .4ghz. Its been tested again and again that you can get to 3.2ghz with a voltage increase of just .01 with a cpu temp increase of 5C on average. If you dont plan on going passed 3.2 and dont want to spend the extra money then dont, but if you see yourself going way passed it then its more of a need issue.

Turbo-mode would take care of the small OC automatically. I think you inadvertantly derailed the discussion (post #8) by mentioning a 4G OC, later taken up by EricPie. My personal opinion is that advocating a 4GHz core Core i7 (especially a c0 step) with a stock Intel cooler should come with a number of proviso's, namely:
-No two CPU's will achieve the same OC given the same voltage
-A big OC achieved using automatic OC utilities invariably adds more voltage than required for stability purposes, whereas an "overclocker" will tweak settings for the minimum amount of voltage required for a stable OC.
-The same utilities will also add voltage to the MCH, so both it and mosfet cooling needs to be of a greater consideration
- Making the distinction between OC via base clock and multipier.

Given that an experienced OC'er will not be phrasing questions as our OP (and a few other viewers present and future) has, I think it likely that OC via utility is a more likely path taken. All the more likely with mobo makers pushing their "OC Genie", "EasyTune" and "TurboV" etc. With that in mind, and the vagaries of individual CPU's, I'd be more than a little hesitent about mentioning a 50% overclock in conjuction with a stock Intel HSF.

I wouldnt advocate a 50% increase of oc for a 24/7 setup with a stock cooler either, but he's asking for something closer to 20% increase.

No two cpu's are the same correct, but I dont think its even worth mentioning this fact with the i7 in the conversation and talking about mild overclocking. If he's buying or have bought an i7 within the last 9 months it would be really hard and rare to even get a C0 stepping cpu. I own a 920 d0 and c0 stepping. The overclock from stock to 3.2 via preset bios settings doesnt take much more voltage at all. Its 3.5ghz and higher where both cpus start to spread themselves out.

To the OP. I'd suggest a thermalright cooler, they're beefy and can keep anything cool that's available now. It will set you back 50 usd but you can also jump to 4ghz easy when you feel up to it. Make sure the height of the coolers wont interfere with the side panel of your case.