I agree the run flats are awful, without the chilli pack apparently they are not as bad as the springs are softer, higher and the wheels are smaller, I'm removing mine next year and putting an Astra spare wheel in the boot.
Does the Astra spare wheel fit? I thought there was a spacesaver option for the Clubman to fit under the rear floor?
I swopped from runflats on my R50 MINI along with a spacesaver spare and it transformed the ride and eliminated the tramlining.