Do yourself a favor and check the speed chart and climb chart for the Ki61. It's nowhere near as uber as the spit16. It's nice but it can be beaten by a 38J easily. I usually am on the Ki end of things so I can vouch.
Its best speed is 15. The speed chart is a chevron strait from 15k to sea level, and mirrored above 15k. You will have speed on it at most if not all alts. You can turn pretty nice but I'd suggest keeping your E up.
N1K2s I've less experience in. I fight them more than I fly 'em. They're easy enough to rope (not loop, but full-out rope) but the problem is their guns. They can get easy snapshots while in the vertical that others might not get. If you don't time the rope right you come down and get a faceful of it. They have amazing climb rate under 5k, above that it sucks horribly, and decreases rapidly with alt. Speed is decent but I can't recall which is faster (N1K2 or 38J). You can turn with 'em for a while if you saddle up. If you enter equal turns get out. If you enter opposite terms you can get some success. If he goes HO and does a sloppy turn every time (90% sure thing if he's in a n1k2) then you got it made. Avoid the HO and saddle up.