It has somewhat recently come to my attention that there are actually options for gcc -march= that sit in between 'generic' and '$CPU'.

Specifically, these are 'x86-64-v2', 'x86-64-v3' and 'x86-64-v4' where each v designates a minimum subset of instructions required for compliance (e.g v2 requires sse3, ssse3 and sse4.1 and 4.2, v3 requires avx, avx2 and fma among others, and v4 requires avx512)

It occurred to me that were Funtoo to offer stage3s built against these as more performant 'generic' stage3 options (in addition to the current 'generic', which I believe would correspond with 'x86-64' or microarchitecture level 1), they could be offered as fallback options in the event that it's not possible to identify the 'correct' or an alternative working stage3, especially when it comes to Intel and their plethora of chips that don't actually meet the requirements for any of the current supported stage3s.

My subarch identification script can very readily be modified to calculate and offer microarchitecture level support if it's unable to identify a specific subarch.