Fowler,
Before I begin, let me issue a disclaimer. I have not yet flown in the Main Arena. Hope to before long. Lack of money at the present time. However, I have been flying H2H for about 6 months or so, trying to learn the game and the performances of each aircraft.
I have read everything of Mathman's that I could find on the net, plus any other information about fighting with the F6F that I could locate. I have the same problem trying to HO the Spit that you do. They outgun you and can outrun you and outturn you at low speeds. They hold all the aces.
But not if you can get them flying fast enough. As Mathman states, between 250 and 300 mph the Hellcat outturns almost every plane in the game. Co-energy is difficult but not impossible, depending on how savy your opponent is.
Deny him the HO if possible, jinking to make him miss. Once you merge, the average Spit pilot is going to haul his mount into a high-g turn to try to get on your six. Don't try to turn with him at this point. Unload the g's off your aircraft, hit WEP and put your nose down. Accelerate to 250 mph, or better yet 300 mph. He will have to fly faster than you to catch you, which is what you want him to do. Watch him. When he has closed the distance to about 1800 to 1900 pull into a high-g, slightly nose-down turn into him. If you do this right, You'll be able to outturn him just long enough to pull lead for a deflection shot. Nothing will blow his cool faster than being "outturned" in his Spit and taking hits.
If you fail to kill him on this pass, unload put your nose down and accelerate back up to 250 mph or faster. Repeat the above maneuver. Don't drop more than one notch of flaps if you feel you need to use them, otherwise they'll cause you to flow too much speed.
I've been using this maneuver a lot lately because it works for me.
Hope it does for you! Let me know how you make out against your buddy!
Regards, Shuckins