Can’t help a lot, but I’m setting up a film project now. I noticed in the Task Manager that for workprints downsized with DaVinci Resolve, a 1080 DNX file loads down Cubase about 10 to 15% (and sometimes much more), whereas a DaVinci-defined 'Youtube 720p" H264 file hovers just under 1%, maybe 2% max peaks. “Vimeo 720” is in between those 2. That’s on my generation one i7-960 system. Any one of those formats flows nicely for me with about 20 tracks of Play 6 and Kontakt, with a total CPU load around 35% at times. I can see the difference in image quality, but the H264 quality is more than OK and nice to look at. I’ve got a 4gb Nvidia 760 series card, X58 motherboard. It’s a 29.97 project, haven’t checked 23.976.
I think the bottom line is that video and audio compete for similar resources that vary somewhat with video format and the particular sub-version thereof, it’s more than just a muscle power thing.