Information on these products can be found [URL=http://www.matrox.com/mga/archive_story/apr2003/mill_pseries.cfm]here at Matrox site[/URL]. PDF files with more information are also available [URL=http://www.nordichardware.se/Millenium-P/Matrox_Millennium_P-Series_BoardRelease_ENG_NE.pdf]here[/URL] and [URL=http://www.nordichardware.se/Millenium-P/Matrox%20Millennium%20P-Series.pdf]here[/URL].
What separates the cards is the multi monitor functionality: P750 supports three monitors while P650 "only" supports two. We understand that the cores of these cards are based on the Parhelia chip that was released last year.
The GPU is now 256 bits though and the memory bus is also only half as wide as the Parhelia. Right now there's only 64 MB models available. Of course this matters less, as these cards are in no way geared towards gamers.
Video editing, CAD, MCAD etc. is the prime targets for these cards.
Thanks to [URL=http://www.nordichardware.com/]Nordichardware[/URL] for the info.