[Moved to the Hardware forum]
its often reversed for people looking for 10bit display. a cheap quadro to run the monitors and a powerful gtx for cuda compute. this can be controlled by the nvidia control panel. rather than mixing quadro and gtx, its more common to see a display i/o card to drive a 10bit full screen playback monitor and let the rest of the screens run from the gtx. if you don't need 10bit out, just stick with the gtx cards. if using multiple gpu's for cuda compute, they don't have to be identical but should be similar in performance.