Chroma and 2 unibrain fire-i

Hi! I need to make chromakey from 2 cameras.

The idea is to have a man and a girl at different places, grab them in jitter with one camera for each, cut them out by chromaKeying (using a couple of green backdrops) and paste them on another film (inside a car, as if the where traveling together). The cameras will be connected together and there will be only one firewire cable to the mac.

I need to buy the cameras, as far as i've seen the unibrain are good and cheap options but my concern is the FPS and colormodes.. would i have problems with YUV mode and chromakey under 30 fps? or should i use RGB at 15 fps?

Any suggestions for my setup? everything will be processed on a single mac. It would be a 1.67 powerbook G4 with 1gb RAM ATI AGP 128 MB, or a macbook pro 17" 2GB RA (don't know yet which one to use, need to test).

Anybody have done something similar? the latency is also my concern.

Thanks a lot!

Miguel

PD.- In Mexico we have no info about this nor unibrains, the cameras will be bought in the USA so the information to decide is quite important.