AFAIK the 109G6 should mount an DB605AM amd not an DB605A1 like the G-2 and the C.205V.
The DB605AM was designed to accept the MW50 (1,800hp for take off and 1,700hp at 13,500ft). Max speed was 386mph at 23,000ft.
The G-10 could accept the DB605D or DC with MW50. She had more hp than the AM model (both for take off and at altitude). Max speed was 425mph at 24,000ft.
Why the hell should we have a tweaked 109G-6 like WarBirds? This way there is no need of a G-6. A new variant only to have 2x13mm instead of 2x7,7mm? Please ...
IMHO the G-6 should climb slightly less than a G-2 without WEP and better with WEP (MW50 for the G-6).
While the G-10 should climb better than a G-6 with and without WEP (MW50 for both).