Hi mate, on a 500cr the short muffler makes it a lot more snappy, it makes more at the very bottom, revs quicker etc, if you run the wr muffler it makes a little less right off the bottom, less mid range and top but a lot easier to ride and mostly quicker lap times, for me anyway. If it was a 430 the short cr muffler is the way to go unless is muddy.
Kt