It's like night and day! I was using 6.5 and a demo version of 7 on my 2.0ghz MacBook Pro, and the performance in rosetta was terrible. When I got CS3, everything was more responsive, much less "adaptive resolution" degrading when scrubbing the timeline, and render times almost cut in half. Since you're comparing rosetta and your G4, I think you'll be pleasantly suprised!