I think the 39 tooth in the rear is a great improvement. Great bang for the buck. It was only 54.99 and it is lighter than my stock one (aluminum). My new rotors should be here today. Pretty excited about the weekend.
On a side note I also helped a freind with a new tuono put a full Akropovic system and new SBK replica eprom. Holy crap!!! If only my bike would ever run like that. I'm not going to ride his bike anymore. Makes me jealous. Bastard!!!