It's safe to say AH Bf 109G-10 is faster than the P-51 at all alts, but it is also safe to say practically the P-51 is faster than G-10 at all alts to, since the listed top speed is actually a theoretical one and something much more than the maneuverability of 109s can handle.
The listed top speed of AH 109G-10 is about 440mph at 22k (704kph at 6700 meters alt.) but I've never been able to reach actual 440 mph with the G-10 at that alt, but anyhow it does easily go off 400mph speed and more often than not the compression is so bad the speed makes you worry more than be thrilled.
Now, the figure I have on Bf 109K-4 is 727kph(about 454mph), and the figure I have for the Bf 109G-10 is 689kph(about 430mph). So, the figure seems to suggest our 109G-10 is somewhere between an actual 109G-10 and an actual 109K-4. Another thing to take into account is the 109G models, after 1944, have no 'exact' figures in them since there were all sorts of field modifications and experiments in so many 109s that it's pretty difficult to sort them out. There are more than 2~3 types of 109G-6s, and more than 4 types of 109G-14s counting only the most 'famous' and 'standard' field modifications.
In the case of the G-14, a version that was planned to upgrade old G-6s to the standards of G-10 and K-4, the early version records a speed of 665kph(415mph), and the final G-14/AS records 680kph(425mph). So in theory, though no actual proof exists, a it is more than possible that a G-10 that is almost near to the standards of 109K MIGHT HAVE existed.
Now I don't know if HTC has taken this into account when they put in the G-10, but I think it is to be viewed as a G-10 that responds to the fans' request for a 109K-4. A 109G that performs as fast as a 109K, but doesn't have the minor arrangements in aerodynamics the Kurfurst has.