Here's what I came up with. This is very hacky and unreliable, but get the CPUID with;

cpuid -r | grep "0x00000001 0x00" | awk '{ print $3}' | uniq | cut -d x -f 3

then grab MCE (thanks Max for the suggestion) from https://github.com/platomav/MCExtractor

unzip MCExtractor-master.zip

cd MCExtractor-master

chmod +x MCE.py

dos2unix MCE.py

./MCE.py /lib/firmware/amd-ucode/*bin

(at this stage it complained about missing dev-python/colorama and dev-python/prettytable, so i had to emerge them)

Then press enter and it dumps out CPUID and version for each file.

Other than case differences i found the CPUID for my fam10 AMD system. eg

# cpuid -r | grep "0x00000001 0x00" | awk '{ print $3}' | uniq | cut -d x -f 3
00100f43

And in the MCE output;

| 4  | 00100F43 | 010000C8 | 2010-03-11 |  Latest  |

Dmesg had

microcode: CPU0: patch_level=0x010000c8

So its confirmed its at the latest microcode, from 2010