So, it seems like there was still space for the new CPUs in a 16mb BIOS after all.
My 1800x OC
Win10 Pro / PRIME X370 PRO / 1800x @ 4.05Ghz - BIOS 4012
TPUII / 40.5x / 1.425v Vcore / SOC 1v
CPU LLC3 and SOC LLC3 / CPU and SOC Phase control = Extreme / CPU Current Cap. 130% BIAS=CB11.5 (CB15 score 1780)