amd cpu? about the same, per transcode.
do note, its not the encoding that is the bottleneck, it is the DECODING of x265/hevc.
plex does not encode TO x265/hevc, it encodes to x264, which is relatively easy (cpu have been doing that for years now).
you should also read the entire thread @ Plex, 4k, transcoding, and you
the point of having high quality 4k content, is not to transcode it to lesser quality, its to avoid transcoding and direct play it.
finally, hardware transcode requires plex pass, so you will want to take that into consideration in whatever your final solution is.
