The G-14 is underpowered currently in AH:
109G-14 Bug threadBut the it should hit 410-415 mph at 16400ft (FtH)
The K-4 top speed is 452 mph or so and has a higher FTH due to the larger DB603 supercharger. The G-10 (not the old AH G-10, that has always had K-4 performance) should hit about 425 mph or so and have a higher FTH then the G-14 (same engine and supercharger as the K-4 = DB605DM w/ DB603 SC).
G-6 = DB605A
G-6/AS = DB605AS (with DB603 supercharger)
G-14= DB605AM (M = MW-50 = water-mathanol 'emergency power')
G-14/AS = DB605ASM (with DB603 supercharger; M = MW-50 = water-mathanol 'emergency power')
G-10 = DB605DM (with DB603 supercharger; M = MW-50 = water-mathanol 'emergency power')
K-4 = DB605DM (with DB603 supercharger; M = MW-50 = water-mathanol 'emergency power')
The G-14 is basically a G-6 with water-methanol injection. This means it's faster then the G-6 on emergency power. At C/C power (AH = MIL power) its just slightly faster then the G-6 at altitude.
The AS and DB605Ds had a larger supercharger that gave better power up high, thus the higher FTH. In the case of the DB605AS and DB605ASM, the standard DB605A / DB605AM gave better power down low.
What the G-14 does is fill the gap between the G-6 and K-4. Once it gets fixed its strengths will become obvious, especially against the the new Spitfires.