Reminds me of the famous thread on stack overflow. I'll link the rust one directly, but one cpp answer claims 283 GB/s - and others are in the ballpark of 50GB/s.

The rust one claims around 3GB/s

https://codegolf.stackexchange.com/a/217455

You can take this much further! I think throughput is a great way to measure it.

Things like pre-allocation, no branching, constants, simd, etc