OK, I tested the Bf109G-10 offline. I climbed to 22,100ft, set autolevel on and turned on the WEP. At about 300mph indicated I turned on the film recorder. I let it accelerate while I made a sandwich. After about 7.5 minuted I turned off the film recorder. The speed indicated at that time looked to be about 445mph.
When I reviewed the film it appeared that it took about a minute to reach 420mph from 300mph. After about three minutes the speed was pegged at 450mph, where it remained for the rest of the film. I don't know what the optimum altitude is for the Bf109G-10's best speed, but 450mph isn't far off of 452mph.
In regards to the Bf109K-4, I doubt that it will match the Spitfire Mk XIV. Frankly I can't see how the Bf109K-4 would even warrant being perked. In comparison with the Bf109G-10 it would handle a little better at high speed and have a slightly different list of armament options, but otherwise it would be largely the same aircraft.
I would like to see it added, but I can't see it's performance earning it the curse of a perk tag.