I've been told the Carbonion give's no real power gains.
My past experience on a 1.8T Audi TT engine was that the only thing that really worked well, was a forced air induction setup, air rams / scoops at the front of the vehicle (behind the grills), straight into an enclosed free flow filter, then on it a oversize MAF housing.
Through the winter it make a mild difference, but through the summer, you really see a drop in the intake temperature, therefore denser air pushed through the turbo and more power.......in theory.
Not sure anyone has this type of thing on the Golf, but on the Audi we had a device called 'Liquid TT' which was a realtime datalogger / Stat's display, so I noted a 10degree difference in intake temperature with the induction kit.
Intercooler also makes a difference when couple with an induction kit.
Obviously I could be taking total rubbish, but the above is just my experience on former projects.
Robert