Thanks Jabo sir.
From what I understand the Ki-44 is the old flightmodel, but an error crept into the code regarding the engine. So instead of boost1 becoming the new "100% throttle", at 100% throttle the ki-44 still produces full normal engine power, and the additional boost stages will pretty much be added as super-WEP. This is why this FM (flightmodel) can achieve such great climb rate and top speed now.
I'm not 100% sure it's true, but at least this is what I believe. The same phenomenon can also be seen in the Spitfire IXe. Both these models are awaiting a complete overhaul though.
Cheers!
/Robert
XO 4th FG
P.S. The 4th Kokutai will most likely be flying the Ki-44 in frame 5