I tried taking the latest BIOS from Supermicro on a test machine in the lab, but the microcode still differs between core 0 and 1-7. 

Every C2700 series machine I've checked also has this microcode behavior, so I'm guessing that its going to get acknowledged as a bug.  These processor is extremely common and HCL for vSphere 7, so I'm guessing we will see a patch soon.