The person who ran the tests used hacked drivers to get above the limit of two simultaneous transcodes for GTX cards. Read the notes, search for “session limits.”
Regarding your CPU, I’ve no idea (I don’t transcode 4K). The video transcoding will occur on the GPU. However, the CPU will still be used for things like audio transcoding and packing the audio and video streams together if direct streaming is used instead of direct play (mkv → mp4 repackaging, etc). None of those tasks are heavy hitters on the CPU, but you’ll hit a limit at some point.
This thread might have more info you can use:
