Should I be concerned about what seems to be a downgrade from the C9 to the CX in terms of 10-bit (vs 12-bit) 4k support ?
Any other downgrades ?
There are no 12 bit consumer displays anyway so no you should not be concerned, also the HDMI 2.1 ports on the CX are 40Gbps were as the C9 are capable off 48Gbps but in real world usage this will not be an issue.