Speed and climb would be averaged at 5k, 15k, and 25k, just like I suggested. The low, med, and high alts would all be averaged.
The thing is, currently, the ENY calues are pulled out of the air (or so it seems). They is no apperant rating system at all other than "it is fast" or "it has 4 20mm guns", etc. The stats that can be valued and applied to a scoring system should be, IMO. Once values are applied to all the aircraft, THEN the attributes that are not rated can be brought into effect and the "judges" can apply whatever fuzzy logic they wish. At least they would have a starting point as cold hard performance stats cant be denied (plane B can move X fast). Thanks to Karnak for bringing to light a "category" I had over-looked: compression.
Roll rate. (190 vs Spit I, etc)
Dmg absorbtion. (Spit vs 190, etc)
Ease of Use (Spit16 vs P38, etc)
Compression problems. (109, P38, vs P47, 190, etc)
For instance, take the 60 or so fighter aircraft in AH2 and simply divide the list by 10 in each category. I just happen have the turn list (no flaps) right in front of me so both zekes, Hurri I, Hurry IIc, Spit I, and Spit V would all get the best rate in turning: a "1". The next six would get a "2" (Hurri IID, FM2, Seafire, Spit8, Spit9, Spit16). The next six would get a "3" (Ki84, F4F, 190E4, Ki61, 110C-4, 109F4). And so on. This would be repeated with each and every category that is already established in a statistical manner. Average speed (5k, 15k, 25k), guns, ord ability, average climb rate (5k, 15k, 25k), etc. Oh, and what about acceleration??? That is well published. Another category to rate.
I've taken the liberty to just see how the planes score when compared to my very preliminary scoring system. I didnt take into account any of the "un-scoreable" data such as roll rate, compression, etc. Just the cold hard facts. Of the four planes I scored (P38J/L, the P47D-40, and the Fw190F-8), all would receive a lower number ENY based on the values alone. Those aircraft's speed, firepower, and ability to carry massed ord vaulted them up a few notches on the ENY scale. The only thing those aircraft cant really do well is... turn.
A quick bit on the way I scored the ENY. Since the ENY spread is 0-50, I simply converted the rating scale to 1-10 for scoring (Formula: 50 divided by 10 times scoring rate = ENY). Something with an average scoring "rate" of 5.5 is going to receive a 27.5 ENY (28). Something with a scoring "rate" of 7 will receive a 35 ENY. Under my formula proposal, the scoring will be more dynamic and the ENY spread will be greater. The C47 will get the 50 ENY, of course. Aircraft like the lowly Hurricane I and P40B would probably get the 45 ENY... but I dunno, I have yet to score them.

Also, I'm not sure how the absence of ords for fighters would effect their ENY, that is something I'd have to brainstorm about. Hmm.
Some hard stats would have to be recorded like range and massed ords. I'd volunteer to up each and every fighter to determine the range on a full tank plus DT (if DT available) and convert to other than 1.0 burn rate if need be.
