In all fairness I have to say that the K&N mushroom filter can ultimately flow more air than the GSR induction kit. But even then the GSR induction kit gives more power. The reason for the higher performance figures of the GSR kit is that it is designed not only for a moderate flow but even more so using the puls charge effect, which helps to increase the volumetric efficiency at rpm that are realistic on the standard or fast road engine.
The K&N will show its advantage well over 9,000rpm where the air is moving so fast that the puls charge effect doesn't come into effect anymore.
The downfall of the K&N is that it is far too pricey whether induction kit or filter and most of the induction kits are just thrown together, which doesn't warrant the price tag.
That the K&N made on your (Jai's) turbo a difference does not allow the conclusion that it would make a difference in the wanted way on a normally aspirated engine as the induction design needs to be totally different between the 2 types of induction.
To get the best out of a normally aspirated engine the only way to go without compromise is a sequential set-up, but nobady wants to pay for it the money it costs to produce. Therefore the very good fast road applications will be produced as they are.