I have a self-propelled Honda Harmony mower now. It has a 3-speed transmission, and the max speed is rated at 3.2 mph. I find this to be terribly slow, and despite the weight of the mower I can push it faster than the fastest speed (does get tiring after a while though). I am looking at Toro commercial units for next season. Their top speed is 4.2 mph. Wondering, for any of you that have used them, if they go fast enough. This is also the top speed that I have seen for a 21. Looked on JD's website but they don't have the specs listed for speed.