The biggest issue with downloading x265 stuff from the high seas is that so many of them are just x264 that's been re-encoded in x265, resulting in smaller file sizes but reduced quality as well. x265 is superior in almost every way technically speaking but it needs a good source material, not an x264 reencode. Their "golden rule" is more like a rule of thumb and I absolutely wouldn't use some blanket criteria like resolution or dynamic range.