One thing I notice the most is the lightning quick backshifting. So if you come off a little jump while in deep snow and keep it pinned, the engine rpms will stay nearly constant and clutches will shift to adjust to the changing load/track speed. Same if you're off and then back on the throttle, rpms recover much much quicker than stock. The performance is no where near what a stock clutch is at. If your buddies figure their stockers are hot, they will crap when to ride one that is Dj equipped (and properly tuned), I would be happy to ride with your group do demonstrate.
This is an old story now, but last year we had to identical 163's in Revy, we even set up the rear skid with a tape measure to ensure everything was set up the same. One ran stock clutching the other one DJ's kit. In over 3 feet of powder stocker pulled around 62 km/hr trackspeed (on the max speed gauge), same runs the DJ equipped sled pullled 82 km/hr, results varied all weekend from 15-20 km/hr difference between the two (swapping riders and varying conditions). Yes, the stocker one now has DJ kit and performance of the two now are equal....at least now it is operator dependant
Clutch maintenance and sled set up also come into play, as I've seen people throw in a kit and expect the world after riding mine. Even with a DJ kit, you still have to service these clutches and keep them clean, keep belt tension up, proper chain and track tension, regardless of whether there's a clutch kit or not. But regarding belt life....i just changed my first belt out after about 1500km's...it didn't fail, it is now my spare, figured it served it's useful life and can now break in the new one. Sorry for long post...lots to say about the gains from clutch kits.