rewire works pretty well for sending midi to max and routing audio from max into logic. the timing with the IAC bus is rubbish. vst plugins are pretty good for timing and stability (rewire can be a bit unstable with logic) but obviously you cant edit them easily.
rewire seems more stable with ableton for some reason.
a problem with logic is using synch information. tick info seems to be quite innacurate when it arrives in max. i couldnt use it really. ableton seems a bit easier to synch.
i use 1.25 ghz powerbook , logic 6.3.1, live 6, os x 10.4.8
also... if youre concerned about super tight timing, only certain bpms will give you accurate results. these are multiples of the vector size in max. other bpms will noticeably drift a few ms using rewire