After doing lots of reading up on performance filters and reading lots of independent tests. The pressure drop from a performance filter to a paper filter was 0.09%. Basically there was hardly any difference with flow rates and the papers ability to supply enough air. A paper filter will always filter better than a performance filter. I ran my car with a K&N panel filter, then switched to the paper and the car ran better with the paper at stage 2+. I found I had small boost fluctuations but with the paper filter they disappeared. I would presume it was down to turbulent air going over the maf sensor.
The main restriction with the oe air intake is not the filter. You have to look into other restrictions such as intake tubing, intercooler design, cylinder head design and valve design restrictions. So simply fitting an after market filter will not improve things any.
