THe Ki84 has the ability to take off with 50% fuel loaded with 2x DTs or 1000#'s of bombs at +/-60 mph and initially climb out at around 3k fpm. This, not speed, is the KI94s special power.
Just before the KI84 came out I had been playing in Spit 1 a lot. Just my own personal observation of the KI84 is that with the flaps out the Ki84 feels like a Spit 1 that can climb.
If you get a good advantage on a LA7, he will typically dive and run. If an engagement goes bad while in a KI84, you can climb. This is the difference for me. In KI84 I will not attempt to chase the LA7's, this is not the fight I want. 400 yards or so out I climb and hard. Hopefully they come back, and they almost always do.
Anyway I have fun with the KI84. It is a pleasure to fly and die in - Love it hate it, it's your quarter.