what would be the max recording times to a 256 GB drive for 4k,30p video at-
1) 8 bit, 420, 100 Mbps, Interframe
2) 10 bit, 420, ? Mbps, Interframe
3) 10 bit, 422, 150 Mbps, Interframe
4) 10 bit, 422, 400 Mbps, ALL- Intra

UPDATE- I just found an article on this subject at
http://www.capetowntours.photography/best-memory-cards-panasonic-gh5/

Their answers were for a 64 GB memory card.
1) 85 minutes
2) no answer
3) 56 minutes
4) 21 minutes

Are these numbers correct?

I record UHD 60P so 8 bit 4:2:0 at 150Mbps on my GH5 and get around 1hour 50 mins on a 128G card. So you should get more than double that for a 256G at 100Mbps. So those numbers look about right.