Only the Mac Pro is Core i7; all the others (oddly, IMO) are still Core 2. If what you want to do with your Mac is CPU-bound (or, especially, memory-bandwidth-bound), then even the cheapest Mac Pro will significantly outperform even the 3.06GHz Imac: by 50% per core, if you believe Apple's benchmarks, and of course you get twice as many cores, plus hyperthreading.

This also means that the new Mac Pro tops my own threshold of "a computer needs to be three times as fast before it's worth upgrading", but actually maybe it's that rule of thumb that's now wrong, 'cos there still seems to be plenty of go in my current one.

Peter