I run a 2.1ghz G5 with 1.5gb ram, and reaktor 5.1 doesnt peg my CPU up past 39%. My iBook G4 1.33ghz with 512mb ram doesnt get pushed past 66%.

It really depends on your CPU, its cache, and its frontside bus.

ram is suitable if you're doing a lot of work with samples and raw audio and such.

When I work with reaktor, I usually bounce my results down to audio, then work with it there. Reaktor hogs waaaaay too much CPU to be practical to use more than a couple instances of.

I appologize for ending that last sentence in a preposition.