My son had a KTM 350 EXC-F. It is street legal. He won a race in Baja with it. He now has a 450XC-W which is a real race bike. It is hard to ride because it has almost no flywheel and the motor hits very hard.
Hands down the 350 is a sweeter bike to do most things with. Very easy to ride well, according to him. Plus it's pretty fast.
Straight ahead and faster -Bo Weaver 1970
"There I was..." -Griffin Niner Three Hotel
"One day closer to a parade..." Jonny Gomes, spring training 2013