Some of last tours stats (forgive me if I do not recall ENY values)
109K4 10,424 kills with 1.56 K/D 20 ENY
F4U-1C 5,780 kills with 2.95 K/D Perked
N1K2 12,084 kills with 1.16 K/D 5(?) ENY
P51D 31,518 kills with K/D of 1.37 8 (?) ENY
Spitfire XIV 1,121 kills with K/D 1.37 Perked
Spitfire XVI 19,355 kills with K/D 1.11 5 ENY
Tempest 2,933 kills with K/D of 6 Perked
The below chart breaks down the percentage of the total number of aerial victories these planes had in relationship with each other based on last tours #s, 341K kills or so.
So, there are three ways of looking at the issue, kills, performance, usage.
On kills alone, Pony D needs to be perked, not the 1c.
On performance, lets skip that for a second....
On usage, well if I recall correctly the F4U-1c was not perked when introduced, it was perked because it became "the" airplane. This is what I have heard, not sure. Afterall it is the same as a 1d with a 10 IIRC ENY, except the cannons. Should the planes that are used the most and responsible for the bulk of kills be perked or have their eny lowered?
So, back to performance. First assumption is that the planes in question are flown within their envelop against planes with similar characteristics. I hate to beat up the anti-brewster guys, but you get killed falling into the brewsters fight. P-51, K4, and Spit XIV and even the spit XVI (close stats) are similar to the K4 in straight line tests, but in turning the K4 falls short. (Using hammers website
http://www.gonzoville.com/charts/index.php ) The Spit XIV has a no flap turn radius 70 feet tighter than a K4 (16 is 130 feet tighter). So, to most pilots out there, the bulk of the guys in the MA, the spits will dominate the K4, as they will tend to devolve into a turn fight. Now to the pony needs to be perked guys, the P-51D has performance numbers drastically lower than these other airplane except speed. Even there it falls short to the K4 and XIV at most altitudes.
Anyway, regardless of how you slice the stats, there is not one plane that dominates all flight envelops for most pilots.
As to the K4 being 20 ENY. Well, I am glad it is there at that level. It gives you a chance to fly a plane with LW performance even when ENY is stacked against you. Because the K4 is pretty much all I fly, the XIV does not concern me as much as another K4.
I would propose that the perk system wander around like eny does after every tour. Whichever airframes are responsible for the bulk of the kills, then their eny is altered. If there is a perk ride that sits unused like the XIV, then lower the ENY until it starts being used more. Perkies were meant to be spent. It is not like any of the perk rides except the jet and the rocket plane, are really that decisive to most pilots.