Video codec and hardware advice needed for multi stream and screen playback

Hi All,

I'm building an installation that requires about 8 hours of 720x540 video to be played back in different ways. The videos are a collection of 5 min interviews and for each one there has been some profile footage shot (side on, front etc). The idea is to have around 20 of the clips spread accross 4 1920x1080 projectors (projecting onto a curved 270 arc) playing at any one time. Normally this will be 1 person speaking and the rest displaying the profile footage but at times 20 clips may fade in and say the same word at the same time.

I've been advised the best way to go with this is a single video card (ATI Radeon 4870) and two matrox2go's - by using one computer (beefed up mac pro) and one card I don't need to genlock or worry about syncying the sound and video from different machines.

Does anyone have any experience or insights into anything like this? will I be able to play that many streams ok in QC? will I need a RAM disk? (and a lot of ram? how much) and if so what is the best video codec to use - whats the best trade off between smaller more compressed clips I can fit in fast ram vs decoding costs?

Do I need 8 cores or will 4 be fine as most of the work will be on the video card?

Cheers for any help/advice anyone can offer