Got some new 15x8 shoes, really happy with the offset:

Also swapped out the 6kg/mm springs in the front for some 8kg/mm ones. I did a rough calculation and found the car would sit approx 40mm higher with this change, so I ordered a 150mm spring (replacing a 200mm spring) as I was already almost at the bottom of the adjustment perch.
Long story short; the new springs look like they will be okay but they aren't captive at the full unloaded shock length, I don't think it will be an issue for track work. If I want to go significantly lower I will probably have to get helper springs.
Itching to hit the track again!!