With no graphics card specific compilation to the ffmpeg, which among intel or AMD is better for executing
ffmpeg -i input -c:v libx265 -crf 26 -preset fast -c:a aac -b:a 128k output.mp4
Would tight integration between amd cpu + gpu help in this case?
Fyi. Currently i am using intel with cpu only mode for this and its pretty slow.
As far as I know and could look up on short notice, libx265 does not make use of GPU computing (via CUDA or otherwise), so the answer to your second question
is almost certainly no.
Performance wise, the ffmpeg command you posted will be completely dominated by the video encoding part through libx265, to the point where everything else is pretty much negligable. Also, the rest of this does not use gpgpu computing either.