I am running a Mk6 GTi and a MK5 Edition 30 ( same engine as Edition 35 )at the moment.
Mk6 averages 30mpg around town and can easily push this to 40-45 mpg on a run
Mk5 Edition 30 averages 28 around town and can push this to 35-40 mpg on a run
Both run on Shell V power
Mk6 definitely more efficient but not as much fun