You should check out the
iPi Software Wiki; I think you'll find a lot of your answers there.
Briefly speaking, you can't expect to get much depth information or tracking accuracy from only two cameras; it will work but only if your character isn't walking around or turning very much. For that kind of motion you need at least four cameras, and now iPi supports as many as six, which may be best for very complicated motions. (I'm using four and it works very well.)
As for the calibration tool, this tool is completely unnecessary for PS3 cameras. It's only for cameras where the FOV is an unknown.
Tracking speed is dependent on your graphics card. For best performance, you'll want a Geforce GTX 250 or better. With my old system using an Geforce 9600GS (I think), capture was about 1 frame per 10 seconds, which was unacceptably slow. With my new computer and a GTX 260 card, I'm getting better than 1 frame per second. Users with a GTX 480 have reported tracking 4 or more frames per second. Now that's pretty fast!
G.