best place to read about compatibility is the media 100 web site. although they cannot test every vendor's Configurations, the compatible configurations guide is a help.
also, so is the media 100 website itself a reasonable guide, but i belive it should have greater detail overall.
you will require new a media 100 system if you change to mac pro.
i have 8.2.2 on a dual 2Ghz and will have to buy a new system as i want to go to intel computer as well. i am opting for hd suite which is based on the aja kona 3 card. i will however wait for the media 100 to be universal binary before making my purchase.
you can upgrade to a sd only media 100 on the mac pro if you wish but again you will require a new system.
you will need to keep your current system intact, especially if it works properly and buy yourself a second system or sell your current system to offset the cost of a new one.