The LT500 loves to breath, we tested with a 39 air striker and 6" K&N and went with 41 mm and went with a 9" K&N and picked up over 3HP over all using Rouges Air Filter Bracket
I just wish the bracket could of panned out. The v2 was very nice, but the fabricator(s) just made it too expensive to sell suzukiquadracerhq
Also agree that if you go to the sand the open system will gain you some power on the top end. Good luck!