This may be a bit opaque to some; KArnak's statement. Does everybody get that when you look at, for example, Mosq's turn rate hierarchy, that you're looking at steady-state turn with no alt loss at a known loading and flap condition?
To get no alt loss and best turn, you're generally at a severe bank angle and something close to either CLMax OR, at least, the best CL you can get without decelerating, ie, you're either stall or power limited. It is also true that you can exceed the steady state turn rate by turning your lift vector such (by banking) that you lose alt.
As for that K4, its turning ability isn't that bad. REferring to the Mosq chart cited above (I want to say a hint less than 20 dps at 25% fuel, no flap), you'll find it can indeed turn with some of 'em.In fact, I'd call it a Pony Killer, since the Pony can't outclimb it, outrun it (alt dependent), or outturn it. I always up it when I get tired of Runstang tactics. As for the gun, I too have been frustrated, at times, with the 30's poor ballistics caused by its low muzzle velocity. However, I also note that, firing straight up or straight down, there is no need to compensate for drop. Indeed, I was shocked at how easy it is to flame a B-17 from directly above or below yesterday. The coolest thing is, if you're carrying enough speed (and the k-4 has plenty), you can approach the bomber from a very low 6, staying out of gun range, get below and ahead, then pull vertical and take your shot. The tricky part: if you don't pull out of the zoom, you might just find yourself hanging by your prop at low velocity a couple of hundred meters above the formation. Even so, if you pull off before you get above and with decent speed, you're still not that easy a target. Plus, the tactic seems unexpected, at least in the couple of trials I ran yesterday.
I'm still waiting for the dude who wrote that Spits are easy to kill... I'd say, as encountered, they can often be BnZed, if you're a good shot (I'm not, especially). I'd also say that, if you dogfight them, generally you are dead, dead, dead. However, it seems like that guy was an FM2 fan. Spitty can out run it and is the energy fighter in an FM-Spit encounter.