i7 920 user here.
Mine is air cooled Monsoon Vigor III, 3.8Ghz with NO voltage mods, north of 4.2Ghz with voltage boost. Its the old chip to not D0. Those i7's are totally unbeatable no matter how much you pimp your AMD it can't hang. I mated mine with with a pair 295GTX's and 12GB (upgraded since I made my sig) of dominator memory. Sorry AMD, you don't have anything that comes close to that on air.
You don't need the higher priced model unless you go for the unlocked extreme version otherwise not worth the cost because the 920 delivers tons of performance as is.