here's a link with some benchmarks (including an ae render benchmark) comparing a newer 3.2ghz & 2.8ghz, along with some older macs. hopefully that can help you figure out what's right for you...
personally, i think i might go for the 2.8ghz and spend the money on 16gb of ram... rather than a 3.2ghz machine with 8gb of ram...
the general order of importance for ae is:
1. cpu speed & number of cores
2. ram
3. drives
ae is a 32-bit application and as such can only address 3gb (although, i believe, theoretical is 4gb... i'm not sure why there is a discrepancy). however, with multiprocessing enabled (or nucleo pro) ae can launch a render engine fro each processor and each render engine can address it's own ram. 2gb per render engine is what is being recommended, so if you want to get the most out of 8 cores, shoot for 16gb of ram (you can always add ram as you get the chance).
also,
as per this article, you may be able to squeak out as much as a 15% increase in speed if you can fill all 8 ram slots with ram... note, that the test was using a ram benchmark utility and was not a real world test, so take it for what it's worth...
you didn't mention drive setup, what are you planning for your media drives..? sata2 is a good way to go, they are fast and relatively cheap, but you would like to get those on a separate controller (so your media drives won't run on the same internal sata bus as the boot drive), so you will want to look at a separate sata2 card.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW
