I have an 08 154 that is stock except a DJ clutch kit. In our group there is 4 older revs. I easily beat the stock 05-06 151 800's every time. The 06 159 with clutch work I also beat every time but not so easily. The 07 159 with a rider that is 50 lbs less than me is a roll of the dice to see who wins. If we poach tracks we just trade marks until we quit. If we go fresh tracks it seems like he can edge me out more often than I can. Not scientific by any means but just how it plays out for us, it does seem though that for "out of the box" overall performance the 06 sleds have been the most trouble free. They are a good choice for less money.