I just relaced my air filter on my 1.8 Sport for a standard one to find the old one was filthy. I also spotted that the vacuum pipe on teh FPR had come off. I always felt the car was getting out of puff at about 5500rpm - so this should explain it.
I'll take the car for a drive later and I'm expecting to notice a small difference.
The lesson here is - if you want more power, make sure everything is working properly already!