I've had a couple BSM's and one Carbon, and a couple blacks in other brands.., I would vote for the Black Sapphire. I always go back to that. Can't go wrong with either, but I wouldn't expect the Carbon to break up the black much. If anything, it might clash with the black, whenever you do see the blue. Carbon black will often look black anyway, just not as rich a black as BSM. It does look beautiful in good sunlight though and you're gonna get a lot of votes for it from guys on here with Carbon Black, shadow line and black wheels etc.
Like I said, can't go wrong, both awesome on any car.
Here are some threads you may find helpful. There are several others if you search.
BSM - 2019 X5 50i Lease Takeover
https://g05.bimmerpost.com/forums/sh....php?t=1678287
F15 to G05...my new carbon black
https://g05.bimmerpost.com/forums/sh....php?t=1658214
Black Sapphire vs Carbon Black
https://g05.bimmerpost.com/forums/sh....php?t=1665166