I decide to run some test for my self and share the results with findings, The sample footage is from the old 5D Mark III 1080 30P.
Render out to MAGIX AVC MP4 for me 53 frames CPU loads 100% solid
Render out to MainConcept MPEG2 got me 125 frames CPU loads 100% solid
Render out to SONY AVC Bluray 16Mbps got just above real time CPU load 37% solid
Render out to SONY MXF got me 53 frames CPU loads 100% solid
Render out to SONY XAVC/XAVCS got me 70 frames CPU loads 68% solid
Render out to Magic Intermediate got me 113 frames CPU load only at 27% solid.
These are the most common codecs being use by people. Sony AVC is the slow one. I suggest people not using it. As you can see. CPU render only did really well with Threadripper on a variety of codecs. Ripping thru like a freight train . :)