Find a late model used EXC KTM or Husaberg w/ a set of SM wheels. Or the factory SM versions of the same bikes. My specific choice would be a Husaberg FS570 (looks like this http://www.moto123.com/motorcycle-re...y?artid=122427
). The Berg is smooth, reliable, fast and light at 2/3 or less the price of a 690 - and will dust it on the track.