There is absolutely no reason to perk any Spit we currently have in game.
That, kind Sir, is an opinion.
The Spit 16 is the most capable plane in the game. What else can turn like it, roll like it, climbs as well, accelerates as good, goes as fast as it does, has the firepower it does, and carry the ordnance it does? Sure, some can out dive it, some are faster, very few can out climb it, many carry more ordnance, but the total package the Spit 16 has to offer is tops. If you give all the fighters a score of 1 to 10 for each and every category there is, the Spit 16 would be near the top in all but 2: over-all speed and dive ability. Even then, the Spit 16 is not to be looked over in those 2 categories either.
I wont vouch for a perk on the Spit 16, but I would not flinch it once was placed on it. I'm not sure what HTC just doesn't stretch out the ENY scoring a bit and give planes like the Spit 16, Tempest, 262, or other such uber planes score of LOWER than 5 ENY. Why start at 5???