The i7 is a high end lynnfield cpu, while the 3.3ghz option for the current iMacs are a high end wolfdale chip. The main differences is that wolfdale is based on the older core2duo architecture from intel, while lynnfield is based on the newer nehalem architecture. The wolfdale provides only 2 cpu cores, while the i7 variant of the lynnfield provides 4 processing cores and an additional 4 more virtual cores for 8 cores combined when certain processes take advantage of its hypertherading technology. All in all, the i7 can be up to 5-6x more powerful, but for most normal tasks like web browsing, you won't see any difference.