I can definitely see a difference in bit rate view raw files especially on 4k screen (Macbook Pro Retina), the differences aren't very noticeable on a standard monitor or on Youtube. There is a downside to higher bitrates, such as higher operating temp (not really a problem for the Pano) and increased storage. A 2 minute clip at 21Mbps is about 305MB. For me the best bit rate has been 18Mps, but there isn't a G-sensor calibrated 18Mbps yet.
@Sungmoon Jang can shed some light on the upcoming changes, and hopefully more options in the g-sensor calibrated code. To answer your question though, yes, LPs are easier to read with higher bit rates, but not my much comparing 15-21Mbps. Here is a sample of the 15Mpbs at night, be sure to watch in 1080p.