Have AMD or Nvidia tried pipelining as a MGPU solution? That is, having different cards handle different parts of the render process in sequence. For instance, if you have three cards, the first card could handle the basic t&l, then the second card could handle Hairworks, and the third could handle ray tracing, which would then be output to the monitor. This would negate the microstutter so prevalent in MGPU setups. I remember that you used to be able to hand off PhysX to a separate card but that wasn't in a pipeline but call and return.