... all I can say is do it now!!
Took off my huge superleggeras today and replaced them with some (temporary) Phase 1 15" turbines.
Wow.
The car is so much more nimble, turns in sharper, moves off from a slow/standing start better, no tramlining (well minimal) - ok theres a tiny bit less grip when you nail the throttle but you can adjust for that!
Had to take it a bit easy scrubbing in new tyres but from brief playing down the lanes on the way home Im mighty impressed.. cant wait to cover the first couple hundred miles on the new Eagle F1s so I can really put it through its paces!