What John said, he is Pico.
calculating the trajectory is done less often (servo period) then calculating the software stepping rate (base period). With a hardware stepper ( Mesa or Pico card) then EMC just has to calculate the trajectory and lets the card calculate the step pulses.

I don't have a recommendation for video cards though EMC doesn't need fancy ones.
If you have some, just try them. I'll see if I can dig up someone else's recommendation.

What are you going to control?