I don't like either the 17" or 18" wheels on the GTI, so ordered mine with the 17", which I have already 'presold' to a guy who has just bought an 'ordinary' Golf. Six weeks ago, I bought a brand new set of 18" Interlagos + tyres from a guy in Germany who had just taken delivery of a Scirocco, but wanted some 19" wheels.
I took them to my dealer yesterday, before I disappear on holiday, so that he can fit them to my GTI as soon as it arrives.
Total cost of the swap, about £90