Silo, you may be talking about Ki-100-II.
True, it had supercharger, and it was better than Ki-61 or Ki-100-II at high alt in test.
but it hasn't been mass-produced before the end of the war (only 3 prototypes have been built).
I think that Ki-100-I's high alt performance was common as compared to any Japanese fighters.
Well, oboe,
Ki-100-I is much better than Ki-61-I-Tei (it's known as Ki-61-I-KAIc in AH).
Ki-61-I-KAIc was too heavy in I models, its merit was only it has 20mm cannons.
And, Ki-61-I-KAIc's advantage against Ki-100 is only dive performance, I think.
Ki-100-I's Advantages (almost against Ki-61-I-KAIc):
1) reliable in the war.
2) 105kg lighter than Ki-61-I-KAIc (330kg lighter against Ki-61-II).
3) Better maneuverability and handling by shorter nose, and removed heavy radiator and weight balance.
4) Slower stall speed.
5) Better climb performance.
6) Better power loading by powerful engine.
7) Good dive performance like Ki-61.
8) Good armament. 2 Ho-5 20mm cannon on nose have 250 rounds per gun! (KAIc has 120 rds. per gun)
9) More longer cruising range (1400km without DT, 2200km with 1 DT).
Famous Ki-100 Kills:
244th Sentai's Ki-100-Is have killed 7 F4Us by 3 loss in 1945/6/3.
111st Sentai's 12 Ki-100-Is have killed 11 P-51s by 3 loss in 1945/7/15.
244th Sentai's 10 or more Ki-100-Is have killed 10 F6Fs by 2 loss in 1945/7/25.
244th Sentai's Fighter pilot said "Ki-61 was most good against B-29, but Ki-100 was more good against B-29 and enemy fighters."
so, it would be not best in AH, but be nice plane.

-Mitsu
P.S
If I can, I wanna tell you about Japanese WWII military aircraft references in Japan.
because English Japanese WWII aircraft data has a lot of errors...
But unfortunately, my english is really crappy!

Widewing,
SUPERFLY can make Ki-100 easily by using Ki-61 airframe...
