It's really the same for any video, 4K nothing really new. Rate control average bitrate is essentially how much compression is being done to a video stream during encoding. A small number results in small files at the compromise of quality, high numbers just the opposite. For current consumer H.264 encoded files, often people find something above about 40-50Mbps is difficult to tell the difference in quality. However, it is very dependent on source footage content, original quality, playback equipment, and individual eyes.

Often the first step is to either use the "Profile Analyzer" or view properties of a clip in the media library and replicate your source bitrate.

Jeff