If you're going to ride track the Ktm pro jr is a great bike. The clutch stack is the trick. Ktmtalk can set you straight. My boys were on the Pro jr at 4 At about 5 1/2 went to the pro sr. Now at 7 and 8 are on 65's. They rode the wheels off the ktms. You must change the trans fluid every ride. I used engine ice
to keep them cool
. Bottom line for the track they're hard to beat. They take a little more care, but I never had any major problems. Be carefull if you buy used really check them out. If you start with a good bike ,it's easy to keep up. You can tune the clutch to make the bike hit very hard or more like a race ready pw. If you like the pw and just want bottom end. I would install the qt gear setup . It gives the pw alot of bottom end. Do a search on the internet for pw + qt gears.