a simple remap on a standard GTI will take it above the 230bhp of the ED30.
Do you need to uprate any parts when tuning to that level - gearbox, clutch etc?
Nope. Im running standard clutch and gearbox and have had no problems even after giving it a glaze at Santa Pod. A remap is still within the limits of the parts used on a GTI.
Cool - might look into this in a few months 
Do you find a big difference in mpg?
Nope, not really. Theres all this sale jargon of better MPG and all that but with great power comes great need to go faster more often so the benefits of increased MPG are taken away, but your NEED to push the loud pedal that little bit more frequently evens it all up I found. My average MPG (number 2 on the trip) was about 29.8 (I think, its been months and months and months since I last saw it) but it was in the high 29s. Thats with a good mixture both motorway driving and London traffic.
Long and short, MPG isnt effected (in my case anyway, Id imagine its the same for most other people).
