just like the title says, wahts the best aftermarket kit? or even a custom setup? how about gearing? this will be with stock pipes and maybe a silencer from B&B, the track is studded and hopefully this year ill do some tuning with the jetting.
2001 ZRT 600 LE: 144 studs and a power breather otherwise stock.
A54 with yellow-green or yellow white pri spring and 57-50 helix with a new yel sec spring AND 24-39 gears. Make sure to rev 8500rpm.
edit..it WILL pull it...may take some playing around with weight on the primary...but a good gear to give you amazing midrange pull and top end. I changed back from 24-39 to stock (23-40)(for a day) and the sled was a dog on the traiil..required more throttle!!