I think you’re confused as to what a Blackmagic Card is:
The card does NOT provide any realtime. It’s a card designed to get professional grade digital video in and out of your Mac to professional machines like Digibeta or HDCAM.
Motion, After Effects, etc… do not use the Blacmagic card EXCEPT to give you a SDI video preview to an external monitor. Motion will gain performance by having a beefier DISPLAY card in the Mac (i.e. NVIDIA with DVI out). After Effects will run faster when they make a universal binary for your Mac Pro.