Due to a lower back injury, I cannot ride my ATK more than about 30 minutes, too much bouncing hurts the back. I can ride the XR650L all day on tough trails, but it is not competitive in a tight Enduro because of its size and weight. I am looking for a bike to ride SERA Enduros. I like the Engine feel of the XR650, which has plenty of steady, reliable power. I need a bike with a little more weight than the ATK to ride through, rather than jump or bounce over, those ruts and holes. I am looking at the KTM450 or 520, as well as YZF\WR450 and CRF450. I think the KTM520 would resemble the power of my XR650 and am leaning in that direction, but am looking close at the YZF\WR450. Please comment?