Thanks all for the comments regarding the Ki-61 vs F6F. However, there are more aspects when considering a matchup than just guns and toughness. Unless you are a HO dweeb then that's all you really need to consider.

When a bandit is 100 yards in front of you it does not matter if they have 8 20mm cannons. They can't hit you when you are on their six.
Hellcat should be faster, better zoom climb. And I'd guess better sustained climb, too. Roll rates? High speed I would give advantage to Hellcat, low speeds Ki-61.
Turning ability will be speed dependant but I'd think Ki-61 would have the upper hand at low/medium speeds.
If anyone can confirm or correct me here I'd be interested in knowing.
In WB 2.77, the hellcat must E fight the Ki-61 and use the vertical. Turn fight = dead F6F. Same in AH or ???
Thanks,
Kekule