Well, test drove the alternative vehicle today and have decided to do the swap.
Moving from a three door white GTI with Pan Roof, leather, winter pack and Dynaudio, to a silver three door with leather, winter pack, and the Performance Pack. I've seen very few three doors in silver but actually thought it looked really smart. I also thought the extra performance of the PP was quite noticeable (could all be in my head though). Standard stereo seemed perfectly good and while I think the sunroof looks nice I'd never have actually opened it! It's also one less thing to go wrong / rattle.
Pick up the new car with twenty miles on the clock on Tuesday. Hand back the car with a thousand miles on it.
Fingers crossed that this one's a bit better built than the current one as I really do like the car.
GB