SAME report from here:
Reason rewired into MS works wonderfully.
I did however get to a point where my Reason projects were so deep and complex, that I had to scale down considerably.
It seems like there is always a better way to do it as far as your CPU resources are concerned.
Any program running inside another program is going to hog that power!
10.5.8, Final Cut 6, Digital Performer 7, Mainstage 2, Ableton Live 8, Reason 5, Resolume Avenue, MOTU Ultralight, Genelec Monitors, Fender guitars, Roland Gr-20, Yamaha MIDI drumset, patience.