Good info about the Ed30 vs GTI OEM paper filter. I didn't know that! So it has the same amount of pleats, just not as thick?
330-350hp seems a reasonable restriction limit for the factory airbox. If it were THAT restrictive, paper filters would buckle and distort and the intake tube / airbox would collapse under max boost / rpm, like humans inhaling on a crisp packet.
Here's a curveball then... Niki told me that the drop off in power at the top of my rev range was because of my standard airbox (Stage 2 k03).
Interesting claims with VWR. I've heard that Niki likes the Revo intake. To be honest I don't think an intake alone is going to make a huge difference to the top end of a k03 car. I'll get a better turbo for that, and probably stick an intake on to help it flow a little more while I'm at it.
That looks like a normal K03 curve to me. It does start to run out of puff past 5500 like that anyway and the two lines neatly converge at 6000, where it has little more to give. I can't see an intake making a huge difference, although replacing the standard thing with a big pipe is always going to improve flow into the turbo a bit, well, into the MAF housing at least. You might find perhaps, a realistic 10hp up there with a decent intake on the K03?
Turbo engines are fighting two pressure differentials. The exhaust gases leaving the cylinder, and the boost pressure entering it. The turbo struggling to draw enough air in ranks quite far behind those two challenges and only becomes a factor when they've both been freed off as much as possible. Any power you do find from an intake is always right at the top end, where not that many of us drive at for very long! I can't remember the last time I exceeded 7000rpm!