I don't honestly think this airplane (one of the most widely used in the war) should be considered for being perked at any value.
In my opinion its ENY is actually a little low, but thats my opinion.
Looking at my stats from Tour 35 (december '02) when i had a little more freetime on my hands therefore killed time by playing more often...
Total of 849 kills to 574 deaths.
Of the kills...
Seafire - 225
P-51D - 136
Mosquito - 37
F4U-1D - 30
Hurricane MkIIC - 25
Typhoon - 22
31 as a Ship Gunner
80 in an Ostwind
Generally speaking i flew the Seafire and Hurricane in base/carrier defense situations. The P-51 was used normally as a fighter escort and attacker. Mosquito, F4U, and Typhoon used as ground attackers due to their armament and ordnance capabilities. The gv/ship gun obviously as a last ditch defense effort.
What killed me?
P-51 leads the race with 52
Spit IX next in the pack with 45
LA-7 Next (little bastages) with 38
N1K2/P-38/F6F/SpitV each with 20
D9 and G10 with 15 apiece
Ostwind rounds out with 39 (flying too dang low 'n slow)
Since then my flying style has changed (due to severe boredom with the game) but this is a decent example of complete statistics.
What can be taken is my two primary airplanes that tour, were divided in time between attack/escort mission and strictly defense situations. Tending away from basic "furballing" while trying to get things done with the squadron. Perking Spitfires and P-51's is insane as they are probably the most well known aircraft (and two of the most beautiful) airplanes and when a new pilot logs on they're going to want to fly what their hero's flew. I'm sure if you took a survey or recorded the data, P-51's are probably the most frequently flown 'first plane' by new players simply because they are familiar with them. Whether they saw one at an airshow, discovery wings channel, or just flying along (an all too rare but cherished moment none the less).
My vote is to leave the P-51 and Spit IX alone, as well as the niki (though i don't fly it) because its docile enough to handle and is well armored which suits the beginning flyer...and its not invincible (just ask RV6 when he comes up against my Delta Pony).
On another note...(note bold font, avoided the use of caps lock)
The LA-7 is a whole other story. i hate that little bastard. Perk the hell out of it. If the Spit XIV is perked then so is the LA-7 as far as i'm concerned, and I dont fly either. The LA-7 and LA-5 have a similiar relationship to the Typhoon/Tempest i believe. The first version, slightly less powerful and effective than the successor...the Typhoon was somewhat a failure during the war where the Tempest flourished. As the case should be with the younger brother LA-5, and the big brother LA-7. If you're not perking the LA-7, unperk the Tempest.