Not sure if you're still around George, you don't appear to have been on here for about 6 months...
Just seen this post - interesting write-up. I notice you say that the UK Spec rear springs made the back end about an inch higher than when using the J-Spec rear springs; did it ever settle down much at all, or did it remain around an inch higher?
The reason I ask, is that when I replaced the original stock shocks on my UK Spec with Bilstein Sport shocks, it lowered the front end by about 10mm and raised the rear end by about 5mm. This was due to the spring seats on the Bilstein front shocks being 10mm lower than those on the stock UK spec shocks, but on the Bilstein rear shocks, the spring seats are about 5mm higher than those on the stock UK Spec shocks.
As it stands at the moment, the rear end is about an inch (25mm) higher than the front end. It doesn't look bad at all and it rides well, but the thought just crossed my mind that a set of rear J-Spec springs may just level it up - although I don't like the sound of this "suspension chatter".
Just for reference, with Bilstein Sport shocks and stock UK springs, mine (wheel centre to top of the arch) is front 345mm, rear 370mm.