I have a MBP 17" with 2 Gb Ram and I can say that Aperture handles my 1Ds (11 Mp) Raw files rather smoothly, I'd say only about 20-30% slower than my previous Quad desktop w/2.5 Gb Ram and GeForce 7800 GT 256 Mb.
But even after many months of use still I don't like Aperture workflow, preferring the usual external Raw converter (CaptureOne or RawDeveloper, both Universal Binary btw) and Photoshop CS2, or even ACR, depending on the images/requirements.
Lightroom is very nice, but again I don't like the idea to totally change my worflow, considering that I can't stop using Photoshop for most of my images.
I also found that sometimes the original Raw converters (DPP for my 1Ds, Epson Photolier for my R-D1 and I seem to understand Nikon Capture for most Nikon DSLRs) do a better job especially about color rendering.
Aperture admittedly has the best colors of all the third party converters, but it's a rather "close" system.
Anyway regarding your MacBook Pro choice, definitely wait for the next CoreDuo2, maybe they'll even upgrade the graphic card, a very important factor for Aperture which is based on CoreImage.
Ciao
