Back in 2007, I got the full boat (2.8GHz Core 2 Extreme 24") in order to extend the life of it as much as possible. Now it barely made the cutoff for running Mountain Lion (requires Mid 2007 or newer iMac) and I expect that I won't be able to run the next OS on it. It used to be that OS system requirements were based on the capability of your machines (at least 2.8GHz, etc.) but now it's based on the year regardless whether it's a screamer with 3.4GHz i7 or a slower poke with 2.7GHz i5. Unless you require the extra power, I assume more of you are going to get the least capable machine you need due to Apple's dumbing down of OS system requirements.