If all you care about is speed then the 14900k has a small edge in video conversion for hevc and av1 while x265 is pretty much a draw, it does draw quite a bit more power to do so though, so it's still a judgment call.
It doesn't make sense to not use a GPU though, if you think about it to watch any video you always go through hardware acceleration from a GPU, or from special hardware in standalone players, so there is no reason to not use it in conversion, you just have to use good settings.