I'd say the La-7 has about a 50/50 shot at winning a fight with an F4U-4. Maybe a little less than that. Been a while since I did it, so I forgot exactly what the results were, but me and Widewing played around F4U-4 vs La-7 and I don't remember it being a landslide either way.
I'd say a Spixteen would probably have a better than even shot at killing an F4U-4 one on one, if the F4U-4 fought.
But between the F4U-4 and the Spit 14 I'd say the F4U-4 hands down. The Spit 14 shouldn't even be a perk plane.
If the F4U flaps didn't turn it into a Spitfire, I'd say the F4U-4 wouldn't even deserve it.