I know some other folks out there were interested in a heelclicker for their 600 also.
After a whole bunch of playing around with springs, weights and more than a few beers..

Here's the set up that seems to work on my 600 :
1. Stock primary spring.
2. heelclicker weights with the 1.2 in the shoulder.
3. the kit spring in the secondary.
4. And.....(against everyone's advice)
B]the stock[/b] (cheap plastic) spider nut - this really made the diffrence... it keeps
the rpms up in the power band and brought my top speed back up or above
the factory top end and I still get a great grab on the belt with low engagement
- It Rocks Now !!