For air-to-air in Aces High, the Ki-45 wouldn't be any worse or better than Bf110C. As noted, the wingloadings are very close. 110 might again a small advantage in turn radius due in MA-weights due to the fact that it carries sightly more fuel and has slats. Other hand, Ki-45 has a clearly better powerloading and would therefore climb and accelerate better. So overall they'd be very close to each other.
At low altitudes in a flat lufberry, Ki-45 would turn inside the P-38s in Aces High just like the 110C currently does.
Hopefully AH features Ki-45 one day, with a production run of nearly 1700 it was one of the major combat types of the IJAAF.