niklas,
The rate of climb that you quote is from 1,700ft. Most of the initial rates of climb that I've seen for aircraft seem to use the climb rate at 5,000ft, where, of course, the climb rate is reduced.
Garrido,
The typical climb rates I have seen for the Spitfire XIV and Bf109K-4 always put the K-4 as better, but by less that 100ft per minute (usually 80ft per minute more).
As others have noted, the Spitfire XIV is not really a speed demon until it hits higher altitudes.
According to the Russian chart posted by butch2k it doesn't surpass the La-7 until just under 4,000 meters, and then the La-7 surpasses it again at just over 5,000 meters, the Spitfire XIV finally gaining a significant and growing advantage over the La-7 at just over 6,000 meters.
The P-51D is faster than the Spitfire XIV up to just over 6,000 meters, whereafter the Spitfire XIV holds a steady advantage.
The Bf109K-4 holds a speed advantage over the Spitfire XIV to over 7,000 meters. This advantage is particularly strong at 4,000 to 6,750 meters. Above 7,300 meters or so the Spitfire XIV has a large advantage in speed over the Bf109K-4.
Another interesting note is the speaker at the Con who had flown Spitfire XIVs commented that it could not be held in level flight with an IAS above 450 (I don't recall if it was 450mph or 450 knots, mph I think).
The thing about the Spitfire XIV is that it would dominate the arena if it were free, however as an expensive perk (60-70 point) with a Spit14 icon over it, it'll do rather poorly. It isn't fast enough at AH combat altitudes to run from the gangbang that happens to perk planes and with the arena as crowded as it has been lately there are always higher aircraft around, particularly after a fight has been joined.
I think that the Spitfire XIV should be a 15 to 30 point perk, maybe 40 on the outside. It would be the most historically significant (except for the incredible Me262A-1), nuemerically significant and earliest aircraft to be perked.