We have Progressive fork springs in both Spirit 1100s and a set of Progressive 412 HD shocks on one of the Spirit 1100s. The 412 HDs are VERY stiff. If you normally run less than 275 lbs loaded, go with the regular 412s.
Best price I found was at Phat Performance Parts.
2001 Spirit 1100 (his)
2001 Spirit 1100 (hers)
I have Progressive springs on the front and Progressive 412's on the rear. I love them. The bike handles so much better than with the stock springs. Especially the front end dive while braking.
The front end still dives during hard braking, but nothing like the stock springs did. Well worth the money!!