First ride with the new rear springs today and all I can say is "YEA!".
That back end used to pogo worse than the front, stiff and hard. That behavior is GONE. The front stiffness and rebound is much more noticable now that the rear is smooth and compliant.
I rode a rail trail with lots of whoopty-do's and other assorted bumps. I drove the Z hard into all the whoopsies. The front would dig in and pop up as it always has, but the rear just kind of floated behind without adding much of anything in the way of discomfort. I'm far more impressed than I thought I would be. Best C note I've spent in a long time.
I'm very much looking forward to the availability of replacement front springs!