If it was modeled using US 100 octane fuel like it did in the US tests, it would be a very, very popular plane. Right up there with the P-51D but sadly, it's hampered by the Japanese fuel it used and it really did have a negative impact on the performance of the Ki-84.
These are the results of the flights from the Ki-84 tested at Wright Field.
Maximum speed:
363 mph at sea level
427 mph at 20,000 ft
360 mph at 35,000 ft
Cruise speed:
254 mph at 1,500 ft
Climb rate:
4,275 ft/min
Ceiling:
38,000 ft
Normal range (internal fuel 184 US gallons):
780 m at 254 mph
Maximum range (plus 174 US gallons additional fuel):
1,845 m at 173 mph.
ack-ack