www.opennavyfield.com/guides.html
try this website. i see there is a graph shows the true ability and etc of fps. good guide,

The difference is small for the impact

say you have an elite fighter crew that you leveled to 120 AND CLASSED TO ACE AT LEVEL
you would have about 4.67 million true ability
IF you put 236 vets and max experts

Or you have an elite fighter crew that you level to 120 AND WAIT TO CLASS ACE UNTIL 120
you would have about 4.83 million True Ability
IF you put 260 vets and max experts

So the idea is if you are already going to max vet your fighter pilots you can more then likely afford 24 more vets on your crew which means a difference of 160,000 k True ability which it turns out is less than the difference between a base 12 fighter pilot or a base 13 (which is 210,000 k). So the moral of the story is if you are going to cough up the money and the time to do this, make sure you have elites.