Germany is in a bit of a rough spot with BR III Fighter options, with the earlier 109 variants (BR II) having lack-luster air-to-air weapons and payload, the IAR (also BR II) being woefully outclassed in speed, and the Fw 190 family (Germany’s only BR III “fighters”) being outclassed in maneuverability and payload.
Frankly, with their payloads being so nerfed in Enlisted, the Fw 190 family are atrocious. They fly like bricks (despite German pilots claiming they were more maneuverable in low altitude than the 109s) but carry the armament of an interceptor, instead of the multi-role aircraft the Fw 190 really was.
The G-6 would fit nicely into that BR, with it having worse maneuverability than the Soviet Yak-3 and La-5FN, and worse speed and payload than the American P-51D-5 and P-38J-15, but a healthy air-to-air armament and good enough capabilities in both speed and maneuverability to match up well with most enemy fighters. Certainly better than the Fw 190s or BR II fighters that Germany has currently serving the role.
Other suggestions have been made for the Fiat G.55 to move down to BR III, but I think the Fiat would be too strong at BR III. It lacks nothing, with good air-to-air armament, good speed, good maneuverability, and good payload. It would instantly become the best Fighter at BR III, which is not what anybody wants with a BR change.
The other concern when moving something to a new BR is what is left behind. Germany has two superior options already at BR IV, with the aforementioned Fiat G.55 and Bf 109 G-10. The G-6 would not be missed at BR IV, and I seriously doubt it sees much play as it stands.
That’s it. Bf 109 G-6 to BR III