Even the best G10s were about 10mph slower than the K4, and the G10s varied depending on the setup of the plane. Gee, the G14 we already have in-game is only about 20mph slower than a K4. A G10 (the best of the G10s, that is) would only be a handful of MPH faster than the G14 (the more average G10s would only perform as well as the G14 does). And have exactly the same weapons options. Only difference would be above 17k. Again, worse than the K4 we have, it would continue on for higher than the G14 before falling off.
As mentioned so many times by other people, it saw service AFTER the K4, and performed WORSE than the K4. It fills no niche, plugs no holes. The AS models would be much more suitable.