Thanks for all the good info!
Shouldn't fast pans and dolly shots up the bit rate too, since there is so much changing from from frame to frame?
What do you think the perceived advantages of a higher bit-rate will be? Do you think it would visibly affect things like highlight rolloff?
Since 24bit 1080(like our monitors are capable of) is something like 1.1Gbps @24fps, how come blue ray can look so good at much lower bit-rates?
In ALL-I mode each frame is encoded individually, so in VBR mode the bitrate changes acoording to the scene complexity, eg, a scene of trees full of leaves will make the bitrate go higher.
The benefit of high bitrate CBR would be colour grading, especially when you pull a secondary, there might be less blockiness in the shadow and highlight.
I don't think highlight rolloff has anything to do with bitrate, it's mainly gamma curve, which Magic Lantern is working on at the moment. in the upcoming new release, Magic Lantern digital ISO can improve highlight rolloff.
Bluray material usually comes from very high quality & high resolution master (eg, from film scan, RED or Alexa), the encoded quality will definately look better. However I think 5D3 footage after some processing it can look almost the same or even better than some bluray titles. Both Bluray and Canon DSLRs use H264 which is a highly efficient codec, it throws away a lot of data you can't see.