What kind of SIMD instructions were not available? I assume something like AVX512GFNI or SHA x86 intrinsics?

I think if you're in domain of using SIMD, besides base RAM usage of 2-5MB you should not see drastic difference unless you have a lot of allocation traffic. But I guess Rust solved most of this, just wanted to note that specific memory and deployment requirements are usually solvable by changing build and GC settings.