The 65" b8 on offer at the moment looks appealing. Do I care that b8 can't do HDR and HFR concurrently or is that a tech that will be relevant in 2-3yrs+
To be honest, even on the C8, which does support HDR and HFR concurrently, is only capable of doing so on the TV apps. HDMI2.1 will be required in order for HDR and HFR via external sources. This being the case, no current TV is equipped for this.
The C8 does provide better colour graduation over the B8; and I bought the C8 over the B8 for this reason. However, this is likely only noticeable in a side by side comparison. I can't imagine that you'd be disappointed with the B8; it's an amazing TV.