Hi…
I’ll chime in.
I edit frequently with the Matrox Axio and RT.X2 hardware.
I like them, not only for their real time performance boosts, but also for some of the tools they add in software (i.e. advanced color correction and great in Premiere Pro chroma keying, real time matte keys and alpha channel animation keys).
As they are accelerators, they should get faster as you move them to faster computers, so you should always see some benefit with them.
RS-422 control comes not from the cards but from your serial or USB ports via adapters from Addenda electronics.
My $.02.
Alex