I have a 8700. I tossed on a 400Mbps bitrate 4k x265 10bit file and used hardware conversion to play it. I had to convert to 1080p, so your results may differ. The server was able to transcode the video from x265 to x264 and it played with no issue.
intel_gpu_top reported 84% usage. It was a small clip, so I don’t know if that’s high because it was buffering or if that’s the regular usage. So based on my tests I would say you can convert one 4k video to 1080p at a time. Keep in mind the x265 did have a 400Mbps bitrate though.
