So the only differences from the M to R is the electric deck lift, controls on the handles, foot operated park brake and 12 mph vs 10 mph. The speed is really the only thing that I'd want on the R.
Good to hear clumping is not much of an issue. How does the 7 iron disperse the clippings in normal cutting conditions. Do they pretty much evaporate or does it cover the service with a even but ugly canopy of clippings like my XR7 SZ?