Update: So I believe I have now found the right CPU cooler to meet those requirements... the Noctua NH-D14. It's massive: a 900gram heatsink paired with one 140mm and one 120mm premium fan. Many reviewers are saying it is one of the best air-based CPU coolers they've ever used, and also one of the quietest, ranging from 19.8dB down to 12.6dB.
The only catch is whether its 160mm height will fit in my CoolerMaster Storm Sniper case. This is probably a stretch, but if anyone happens to have that case, it would be a big help if you could measure the motherboard tray to side panel distance. Tomorrow I'll see if CoolerMaster can provide that measurement.
http://www.newegg.com/Product/Product.aspx?Item=N82E16835608018
FYI, the Prolimatech Megahalems is widely regarded as the best air cooler on the market at the moment. I'm guessing it will fit in the sniper, but it would be a good idea to check with coolermaster. I'm sure they can provide the measurement you need, or at least confirm whether or not it will fit. You'll need a fan as well. I'm not much of a fan guru so maybe someone can post a link to an efficient, quiet fan that would pair up with this if you choose to get it.
The i7 975 is faster at stock than the rest and provides an unlocked multiplier. That's about it. Unless you're into competitive benching, I honestly don't think that it would be a good buy. You can get the i7 920 up to 3.4 ghz without a sweat, although, for your purposes, it would be fine at stock.