I just put my car on the rollers, ran with standard panel for a bench mark, then fitted the pipercross and got actually a few hp less but it would have been warmer from sitting a few minute. Then I swapped to the K&N and ran again straight away and got about 8hp more than the standard filter. This was with a standard GT1749 turbo at the time, so I would expect effects to be higher with boost raised on a larger unit.
It should be noted that both the pipercross and K&N are oiled filters and I've had to change MAF once for the oil killing it. I now just refresh a standard paper filter more often.