Cat does have a spring upgrade kit for the SS to deal with the problem you mention. Previous posts on this site lead me to believe the good dealers are changing springs under warranty.
You are not going to match a ZR for it's ditch banging ability- the ZL is more trail rider type. The SS is not Super Sport- more like Super Soft in it's ability to bring home the rider in comfort.
Get a Firecat if you want to be sno-crossing every weekend and kick ass during the week.
Get a ZR for a truly great sport sled that rocks.
Get a ZL if you want to trail ride with friends and family with confidence.
Get a ZL SS if you want to ride 500 miles every weekend and have to work all week to pay for it with out feeling pain Monday, Tuesday and part of Wednsday
I have heard that taking the coupling blocks out will give you more suspension travel and less bottoming. Anyone want to weigh in on this?