Lazs, except for 1940 isn't there pretty much a P51 in every "year" set? P51 MkIII, P51A, P51B, P51C, P51D, P51H etc? Each P51 in it's respective year offers the pony guys enough of a speed difference to run away so I don't think it would be much different than what they do right now.
I have no problem with an RPS, so long as it's implemented properly. The perk system would also allow for a guy to buy himself a P51B when it's a "BoB" planeset and then the next planeset evolution would allow him to buy a P51D thereby affording him his running space that he craves.
Does that make sense at all?
-SW