Just another note, for 100% reliability (not stability, but dropped frames and stopped playback) you'll want three drives, one per chain. Two for video and one for audio.
I've used it with a single newer drive, especially 10k RPM drives, but most older 50pin SCSI drives struggle to keep up with playing two streams of video, the seek time is just too long.
I've got a few 15k drives I'm planning to use, so I should have zero problems in that area.