ok, Your DSG GTi will hit 0-60 in 6 secs,using launch control. especially if its been run in (meaning approx 10000+) you have 197 bhp.Revo are the company best for Chipping IMO.£500 giving you estimated 40bhp. Mpg doesnt exsist in a MK5 GTi, its better known as "smiles per gallon".
Expect roughy 26-28 town average, maybe 1 or 2 miles less if chipped.Motorway cruising expect 34-35mpg at 70 mph.Running on 99 octane fuel and not cheap nasty 95 unleaded.
HTH