Its not a cossie, but when my engine for my track car was being mapped, we logged flow rates using a new standard air filter, old air filter, k & n panel filter in the airbox, k&n cone bolted direct to the turbo and an off the shelf induction kit fitted for the car.

There was no distinguishable difference in flow rates. In the end, I used the airbox with k&n panel filter, purely as the k&n was cheaper than a standard filter.

The airbox has has all flaps of plastic etc removed from the inside and the original rubber pipe replaced with a silicone item.

As for driveability, then low end response is slightly better, and less jerky, but the car never really spends any time at low end so its not much of a benefit. On a road car, then I'm sure it wld be better.