I've been trying out CS2 for a few days but it does seem a bit slow on my machine (p4 3ghz Igb RAM) vs CS, the noise reduction feature didn't really do anything spectacular that my Neatimage plug-in couldn't do, control of sharpening is better though.
If it moved at a good fast pace, I'd keep on using CS2 but I've reverted back to CS.
I think you'd benefit from an upgrade, but CS may be a better bet if you can lay your hands on it and you don't have tons of RAM and a fast cpu.
cheers,
Andy