Just changing to a AirGap isn't going to buy you much if anything that you can feel by the seat of your pants. Now port the heads you have and port match an AirGap to the freshly ported heads now your going places and you will feel the difference.
That can be said for the single plane as well, the race starts at 3000rpm and above. lol
It's kinda hard to get a dual plane to flow in the 320cfm range. :D