Exactly my point. The bike wasn't tuned for optimum hp on a dyno to start with. Here is something to think about. People make a baseline pull, put some parts on and "tune for the new parts" and see what they gain. If you didn't tune for the optimum baseline performance then you can't claim that air filter made 6 hp. My buddy made 5 hp with no parts changed by tuning the baseline. Think about it - people port heads and put in cams for 12-15 hp and a filter makes 6 hp?
I have made passes with no air filter just to see what I gain, and it was nothing on a Gen-2. On my Gen-1 I made almost all my passes with no air filter as there was some gain in performance. On my second bike (I race two Gen-2's) I removed the K&N filter and put a stock filter back in. I've gone 154 mph in the 1/4 on that bike in almost 2000 feet of air at a total weight of 695 pounds, stock motor, generic tune with the stock filter. I am very happy with the stock filter and 154 mph.