If you are in the west (mountains) and this is a standard RMK, gear it down as low as you can... even the 800s benefit from this in general and the 600s for sure. Others can tell you what gears work and fit in the chaincase without changing the chain but I think 45 tooth bottom might work if I recall. If it is a quickdrive PRO model then the only ways to gear down are going to 7 tooth drivers (use Axys style drivers with stock pitch to use stock track if 2.86 pitch), or Kurts geardown kit, or TKI or C3(?)... if you are a 144 it may not be as critical to gear down depending on where you ride...
