Polini, and Malossi are the top dogs. Malossi not being quite as good in my opinion. There are several "levels" of performance with both. The cast iron kits are longer lived than the aluminum kits, and Either will require a larger carb, as well as a proper pipe to allow the Kit to work correctly.
Expect to be about 7 hundred in the hole by the time you get a kit tuned.
Start with your cvt for some quick gains, and if you still need more from it... consider a kit/bigger bike.
1500 contra spring, and a Malossi/Polini/Jasil var. will get you between 5, and 10 mph for about 100 bucks.
