Here's our thread on the JRZ RS1 from waaay back in 2012 (whoa). We were part of their testing for this car.
http://www.ft86club.com/forums/showthread.php?t=11759
You posted in there too!
Spring rates are custom. They were 400 lbs/in or 7 kg/mm for that specific set. It was easily better riding than stock on all roads.
- Andrew