This is a portable format that is used for interchange. The performance may matter elsewhere in your system and yet you may still want to create/access protobuf-packaged data?

Are the only two options SIMD in hand-rolled assembler and unbearably slow?

Often Python, with the most critical parts written in a compiled extension module (like this one), offers acceptable performance with enormously less complexity than writing the whole thing in a compiled language.

This. Yes. This is why I clicked on the comments. Exactly

> Optimizing for the last microsecond

I don't see that anywhere. I see "Fast where it counts."