I imagine some of the remaining gap might be places where inline ASM or things like SIMD, AVX, etc, exist. Where there's been more years and a larger set of people optimizing that ASM for x86/64 servers.
> the remaining gap might be places where inline ASM or things like SIMD, AVX, etc, exist
This was one of the takeaways back in 2017 when Cloudflare sampled Qualcomm's very early Centriq ARM server chips.
> At Cloudflare we use an improved version of the library, optimized for 64-bit Intel processors, and although it is written mostly in C, it does use some Intel specific intrinsics. Comparing this optimized version to the generic zlib library wouldn’t be fair. Not to worry, with little effort I adapted the library to work very well on the ARMv8 architecture, with the use of NEON and CRC32 intrinsics. In the process it is twice as fast as the generic library for some files.
https://www.anandtech.com/show/15578/cloud-clash-amazon-grav...
(Apple Silicon blows them away on laptops, of course.)