Is an iMac good enough?
Aperture is fast but PS is quite slow. Need to wait for Universal version. The good thing is that with Aperture I go to PS not that often - only if I need to do something with masking and etc.
Using iMac with standard 128 video, 2G memory, external Iomega 400g for Aperture Library + D200, 100% in RAW.
BTW, I have a memory monitor on almost all the time. Aperture 1.1 is not using a lot. I was very impressed with it. I have almost a gig of memory "free" all the time. Well, when I bring up PS, this changes. And the Lightroom... ahhh...