GRUNHERZ,
Here is what the Brits said about the G-6, Spit 14 dive (and they don't note starting speed or altitude):
Dive
46. During the initial part of the dive, the Me.109G pulls away slightly, but when a speed of 380 m.p.h. is reached, the Spitfire XIV begins to gain on the Me.109G.
That doesn't sound like "easily, until very high speeds are reached".
It sounds like "Slightly widens separation, but is shortly being overtaken and cannot excape".
Now, the Fw190 dives well enough to escape.