Maybe this helps, I created some statistics for my encodes...
Average bitrate of 28
CRF19 / slow / no-sao / 10bit Blu-ray encodes ("regular" movies for me):
5613 kbit/s
That average does include two movies with extreme grain, 14300 and 19000 kbit/s.
Excluding them in the average brings it down to:
4766 kbit/s
Lowest bitrate encode is 2572 kbit/s.
Average bitrate of 27
CRF17 / slow / no-sao / 10bit Blu-ray encodes ("reference" movies for me = very good image quality):
6902 kbit/s
One high grain movie is included (12194 kbit/s).
Average without it:
6699 kbit/s
Lowest bitrate encode is 3777 kbit/s.
These numbers might not seem very low, but you have to consider that these are extremely high quality, transparent or near transparent encodes.
Calculating a similar average for transparent x264 encodes would result in something like 12000-16000 kbit/s.