Can only speak to my situation: my system in use my way but… with that caveat… I drive three HD monitors with no problems yet. 30″ Samsung and 2X Apple. 30″ and 23″. I am using 2 NVIDIA 8800GT boards. System consists of early 2008 Mac Pro, 16GB RAM, G-Speed es RAID, and Final Cut studio with latest software upgrades (OS 10.5.6 and FCP 6.0.5). Just completed a second project in XDCAM ex 1080i 60 with mucho effects. Simultaneously utilized FCP, Motion, Livetype, iPhoto, Photoshop Elements, etc., etc. with no problems whatsoever. No other PCi boards other than the one driving the G-speed es.
Again.. ONLY speaking for my particular configuration and circumstance.