Originally posted by Krusty 
Why not? Because that unevens the playing field. When 2 virtual pilots compete in 2 identical P51Ds the outcome should be up to the pilot skill, NOT the fact that 2 identical planes flew with a large performance disparity.
The planes have limits for a reason. They all have the same limits. If you want a plane that's FASTER fly a different plane. If you want one that's more nimble you fly a different plane. You don't aks HTC to "make my plane faster!! OOh, no! Make mine turn better!!". 
 Yes, the planes do have limits for a reason - its called the aircraft design.  What this would be designed to simulate were the natural variations between individual aircraft of the same type.  These variations were real, and occurred for a number of reasons - the factory in which the aircraft was made, availability of parts, operational considerations, etc. 
I'll give you an example - pop open a Jane's and look up the Me-109G14.  Depending upon when & where it was made, these "identitical" aircraft had 6 different DB605 engine variants, utililizing 2 different power-boosting units, and a variety of ordnance packages including a weirdo 96 x 2Kg bomblets package.  Put 2 of these side by side, and you'd be hard pressed to tell the difference from the outside, but I guarantee you they would perform differently.
Another example: the P38 - throughout the long development of the P38 there were a great number of engine changes, flaps & controls changes, and changes in armament.  The P-38H is essentially a P-38G with a pair of Allison F17s which had another 100hp.  Depending upon when you got your P-38J, you might or might not have the electrically operated dive flaps and the aileron boost system that was developed.  You can find pictures of P-38Ls with both the 10-rocket and the 14-rocket racks on their wings.
I don't see these as 'large performance disparities", and I don't think they make the playing field any more uneven than naturally occurs in combat when  someone comes in with a superior aircraft, energy state, or position.  If 2 identically skilled pilots come up against each other, the guy that has been taking care of his ride has a slight edge over the guy that didn't.  
IMHO I'd like to see the game developed more as a sim than as a furballing XBox, and I think giving pilots the ability to customize and tune their aircraft would help move it that way.  This doesn't stop anybody from upping their La-7, furballing, bail, rinse, and repeat.  What it might also do is provide incentive for people to customize and master a single ride, which might improve some basic skills along the way.   
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