It's not the HP that you should be worried about it's the freakin torque.
Had mine out for it's first ride this weekend just gone at the RIDE 4 KIDS event at Broadford. Unfortunitly the MX track was deemed unsafe (gotta confer with the organisers on that) so we only had the enduro loop to ride. As i had a modern to ride (RM125) i rode that for a couple of laps before i took the 500 out into the bush, which was muddy and with a lot of handcut and off camber hills. The old girl litterally dug trenches every where she went and made my arms 2 foot longer. Can't wait to get it on a big track like Broadford real soon and stretch her legs.