What's the difference in insurance costs between the two (UK market)? I assume the R is in a much higher insurance group than the GTi. Also what about VED (car tax)? Is the R is one of the uber-expensive groups £500 per year?
Insurance groups; from Parkers -
http://www.parkers.co.uk/car-insurance/insurance-groups/Golf R; group 34. GTI (performance pack and non performance pack models); group 29
Insurers use so many factors in calculating premiums these days, the difference in insurance groups isn't really an indication of any likely difference in premium. To see what the difference is in £'s terms, suggest you get a quote for both the GTI and R.
The VED for the R depends on the CO2 emissions and the manufacturers list price (not the price you pay after discounts) of the car including options (CO2 figures below for VW brochure).
If list price is £40k or less;
Manual gearbox (CO2 180 g/km); first year £800, subsequent years; standard rate of £140 per year.
DSG gearbox (CO2 160 g/km); first year £500, subsequent years; standard rate of £140 per year.
If the list price is over £40k; the VED in the first 5 years the standard rate is paid (so years 2-6) increases by 310 per year.
https://www.gov.uk/government/publications/vehicle-excise-duty/vehicle-excise-duty