Cheeky update on this, as I went out for two sessions at Donington this weekend. Im running 255/40/18 on the front and 275/35/19 on the rear, both with matched RE050A tyres (someone tell Ekona, quick )
Before anyone says anything my TCS is probably super sensitive due to the non standard radiuses.
After 2 corners I was already having problems with the stability control firing the front brakes on me, it was actually causing them to lock and threw the car off line. I managed to drive round it for the most part but it seriously affected my enjoyment and Id argue the stability and safety of the car, bad news.
Got back in and pulled all of the ABS plugs and got the slip light to come up, went back out and the difference was astonishing. I only plugged them back in so the missus could drive it home.
Id also add that Ive run spacers on loads of different cars and the Zed was the only one that was adversly affected by it.