My MBP with 2GB RAM deals with Photoshop files in the range up that I use , up to about 90MB max, just great. Opening, resizing etc is fast, filters are reasonably fast depending on what you're trying to do. I personally only occasionally work with anything over about 60MB but just as an informal test I resized one of my photos to 150MB and opened the Lens Correction filter and did a lot of ridiculous tweaking. Hit the button to process and it chewed away on it for a good long time, around three minutes or so. If I were going to be doing a lot of work with large files over 100MB I'd get the Mac Pro.