Boy oh boy, all those wasted hours of macrumors.com may help here.
I recommend going with the lowest end 15" MBP. There's something about a 128 bit bus limiting the effectiveness of more than 256 megs of VRAM. Besides, 500 odd $ for .1ghz processing and 256 VRAM? That's a fair percentage of the total price.
Also, swapping out the HDD from the MBP (while not easy) shouldn't be too hard for anyone that can handle a screwdriver. Nervewracking, like cracking open most laptops. It doesn't void the warranty, there's no seal to tell if you opened up the casing. However, if you break something in there while swapping the drives that won't be covered..so you'd have to put the original drive back before it goes to Applecare.