I was also having stuttering issues. The first suggested fix worked for me, however I couldn't enter full screen after doing that which is not acceptable. I was able to make playback smooth after going into MadVR settings and setting "CPU queue size" and "GPU queue size" to the max. I'm not sure is that is dependent on any other settings I may have changed but it was after changing those that it became smooth. Since OP said the first fix didn't work for him maybe I solved a different issue, but it's worth a shot and for anyone else who may be having the same problem.
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