A little more info: For fast moving fighting motions, PS3 Eye might produce more accurate results because you're recording at 60fps. Also, having full coverage is probably necessary if you're going to be falling down a lot.
In general, however, I haven't had too much trouble with fast motions using Kinect. Here's a capture of my daughter when she was five that was done a couple of years ago--I think it shows what's possible with dual Kinect recording even if it isn't as accurate as using six or more PS3 Eyes.
Mocap Test with Small ChildThe iPi system is really quite good regardless of which configuration you go with. If you can only have one setup, I'd got with the one that gives you the most flexibility. (In my case, that would be 2 to 3 Kinect sensors.)
Hope this helps.
G.