wipass, believe me, I know how you feel.
But it really is more about timing than speed itself. Those N1K pilots time that move so they come up behind the target going straight at about 500~700yards.
Why it seems that they don't lose speed at all, is because, those guys specialize in long range shooting, as much as they specialize in amazing HO attempts. I can do the same move with the G-10 against a faster diving P-51D, and I'll bet any of us can do it with some practice.
However, what I can't do, is give out the long-range spray like they do. I do the same move with a G-10 against a P-51D going fast, and I get a window of shooting opportunity for about 1 second, until the P-51D leaves me behind in the dust, extending further out than 700 yards.
However, those Niki pilots have 900 rounds of quad-20mms. With the tracers turned off, they, spray like mad. And it's not just a blind spray in the general direction like n00bs do. They know how to aim, and aim good.
They don't have a concept of 'saving ammo', or 'waiting for the perfect shot', at all. When they see a chance, they literally spray everything they have until the target dies, or gets damaged, or tries jinking in horror(which, will allow the N1K2 to catch up).
Basically, they've practiced and specialized the traits needed to fight faster planes to the utmost:
1) They practice killer HO shots, to end the fight in the first round.
2) They practice the high speed/early turn/low-yoyo merge.
3) They practice long range gunnery, to increase chance of shooting down extending cons.
They practice those three things again and again and again. Dweebism? Maybe. But at least, it works quite often(until somebody like Leviathan comes with a better maneuvering plane, and uses the exact same moves against them to humiliate them).