right, i wouldn't call me smarted, but i've had experience in wheels on mk3's!
i would say going for 14" as you say, would be the best idea as you dont want to do any arch work! 15" will fit however there is a very likely chance that you will need to do some arch work! i have 15" on my blue mk3 but they do have problems with scrubbing! to be safe, i would say you would realy need a 14" by 6" wide wheel to be safe! that should give you no trouble at all! (IIRC)
as for tyres, i believe the best tyre for a 14" wheel onto a mk3 would be a 185/50/14. well thats what i would fit to 14" anyway! its a 0.07% difference on the rolling radius compared to the G40 wheel!
anyway, i hope that helps and someone else can back me up! or oppose me if they dare !
