I regularly get 50mpg from mine over the summer. A typical long haul of 100+ miles on the motorway will yield about 53mpg.... my best was the other week with 58mpg over about 70 miles.
Does depend on how you drive though, I am sure some of you could travel the same routes and get 40mpg :-P
The combination of being an essential traveler for work and the infestation of speed cameras mean that these days I rarely go over 70mph on the motorway - this does make a lot of difference to the fuel economy!
Whilst you might wonder why I'd care if it was for business... the company pay a flat pence per mile rate. Quite often in the past it was costing me money to travel for work, now its quite often shifted the other way ;-)
I have no idea what a GTI or R could do, but suspect that BIK and MPG would make it more expensive for me and as much as I love my Golf (and I really do!) I don't really want to pay out any more than I have to - its about on the limit of my budget as it is. What took me from Mondeos etc to this was the concept of a lighter car being more fuel efficient (and it is) plus a better depreciation rate reducing the lease costs (also did that) PLUS at the time (2.5 years ago) the BIK rate was super low (mega low compared to a Mondeo!). All of this offset the fact that its a more expensive smaller car.
Its all worked out fine but the upcoming problem is that the BIK rates advance once bracket per year and VW have a slightly increased CO2 figure for current GTD's (post desielgate) that nudges it up. All of this means that another GTD next year will be at least 4 brackets higher than this one AND the lease cost will have increased.
All of this could well be a deal breaker for me as the only thing which hasn't gone up is my salary

Will be looking hard at some different options shortly, which is a shame because if it was just "are you happy with your GTD?" the answer would be absolutely 100% YES! Its all the other factors that put it in doubt.