I think anything that is double-superior (as fast or faster at typical MA alts and more maneuverable) to a great many contemporaries should be perked. Contemporaries meaning for instance, other Late-War(LW) planes in LW arena, not the entire set, Mid-War planes should not be compared to LW planes for these purposes.
For instance Anax, you have the issue exactly backwards about the La7 and Spit16. The Lala's speed by itself of course, is not the deciding factor, it is the fact that it is both faster and more maneuverable at typical MA alts than a great many LW fighters...ballistics, range, etc, are side issues compared to the primary considerations for fighters, energy performance and angles performance
By way of comparison, the D9 is nearly as fast as the La7 at low levels, rolls better, has better range and arguably a better gun package, BUT, because this speed comes at the price of being very nearly the least maneuverable fighter in the game, every other class of fighter in AHII has legitimate strategy (angles fighting) to use against the D9 and thus can't complain about its non-perked status. In another example, the 109K4 would be an excellent candidate for perkage IF it were faster at a little lower level, not dive limited, turned a little better, and had an easier gun package, but together these things make a reasonable case for leaving it free.
From where I stand, unperked La7s make less sense than unperked Tempests; Both are faster than everything else at low levels, but the latter is certainly the poorer dogfighter, easier to kill or put to flight, so what gives?
The Spit16 though is a borderline case, it is definitely awesome in all aspects outside of top-speed, but most LW planes that are not competitive with the Spit16 in a Co-E dogfight can avoid engaging the Spit16 if they keep their speed and SA up.