Poor Video performance in demanding sessions

Is anyone experiencing laggy video performance and stuttering while using demanding sessions? I’m playing back a full size Apple ProRes file, which SB claims is the best file type for video performance. Even if I use a 2nd instance of cubase as a video slave, it still stutters.

I have similar problems , even with less PC-allergic codecs.
I wonder why on earth SB claim that .mov formats should perform well on a PC…even in pro editing software, they are known to be problematic, be it pro res or DNxHD etc.
All I you can do for now is transcode a working copy to mp4 with a minimal bitrate , like 6 mb/s, maybe even a 680 p wide version just to play it in a smallish video window.