The Mac Pro has only three memory channels per CPU but it has 4 physical slots, slot 3 & 4 share one channel.
When installing 4 modules (per CPU) in the Mac Pro it falls back to the slightly ‘slower’ dual channel mode.
Installing 6 (dual CPU) of the same modules your memory will operate in ‘tripple channel’ and perform the best.
Grid will be supported by Adobe, Autodesk and Solidworks applications from launch and at first it is a one to one appliance.. it will change….so im told.
If you need more then 3-4 GPU then Linux is the enchilada