Well here's my notes on my experiences with the k4 so far:
1. It seems to work best when I use tactics similar to what I do with the Dora or A8, meaning I fly it as a BnZ'er.
2. It feels like it turns better than the FW's, (which almost goes without saying), at least it turns well enough to set up some shots, but it's not a turn-fighter by any means.
3. It's great for bomber killing, but like the Dora it's susceptible to radiator damage.
4. Controls get mushy around 400, but at least it doesn't creak like the ki84.
5. Flaps are great for getting over the top of loops and (if I'm desperate) for an extra bit of turn at slower speeds.
6. The 30mm is of course an issue. Best range is at 200ish. I have my convergence set for 300. I'm wary of taking longer shots with it because of the ammo load. Deflection shots are difficult, but not impossible.
Against specific aircraft:
Mustang: Good matchup. Killed 2 the other day with no problem.
Spitsteen: A problem. Not sure if it has any distinct advantages over the 16...maybe climb rate?
Corsair: Haven't had a good fight against a hog yet, but have successfully used e-tactics against them with a Ki84. I expect the K4's climb rate will let me gain energy advantage, although I've yet to try it.
Turnfighters, small birds (Niki, Zeke, Brew): Can't turn with em, can't hit em.
Comments appreciated as always.