Thanks for all the advice so far

KinobeSTew - Thanks for that, i'll keep a note of those tyre sizes
Cherie - can't beat a good speadsheet! I already have 8J cosworth alloys on my car atm so i'm used to the wider track and the occasional tramlining. I don't have any spacers so the hubs are still standard position
My car is already lowered 35mm (the 16" cossies still look tiny inside the arch so going back to 17s will be good)
The guys at Fifteen52 are custom machining the wheels for my car, so will be a pretty awesome one-off set. Can't wait to get these bad boys on the car!