John,
I followed your traumas with interest, as I am considering swapping my rear exit exhaust for a comp one on my X-flow. What dampers did you eventually go for?
I have the spax dampers on my car, but the ride height can't be adjusted. The measurement at the rear wheel arch seems to be around 145 to 150mm. The springs at the rear are soft, according to a couple of chaps at Le Mans, after lots of pushing the cars rear end up and down and sharp intakes of breath. I've considered buying the Leda shocks from James Whitting.
Rgds, Robert