As i know, the g-10 had the same DB 605D as the k-4, but with the old g-airframe (with improved gun cowling, of course). As a result, it was almost as heavy as the k-4, but couldnt run as fast. The g-14 was only a standardised late-production g-6 with Erla canopy and MW50. The AS engines could perform the best at 25-27K (not sure), so the g6/as would fit much better for the events and scenarios as a real high-altitude 109.