To even start you'll need a minimum of 437w TEC reasonably. That way, when you turn the voltage down to about 9 volts you'll still have decent temps. I'm running mine (watercooled TEC & 437w peltier) at 13.5v and get -25C idle and -8C load temps.
If you'd give it about 9 volts, you'd probably get 15C or 20C load temps. You'll need a huge tower cooler, or maybe a Tt big typhoon (I don't know what heatpipe cooler can handle the most heat, you'll have to do some reasearch) and it's still not guaranteed to work. You'll have to design some type of clamp for the peltier to clamp the pelt between the heatsink and a "cold plate" (solid copper plate that goes between the peltier and the processor). The more pressure on the peltier, the better. You'll be dumping a lot of heat into your case, so a tower cooler could theoretically work best since you could duct the exhaust straight out of your case.
Saying all of this, I have no idea what temps you'll get, since I've never pelted on air. But if you do get it working and get somewhat decent temps, take a lot of pics and give a lot of details because there's been a lot of people who wanted to try this but never got around to it.