Don't use the latest nightly then. Use the nightly from 4 months ago that corresponds to today's stable, ensuring that it doesn't have any extra soundness patches that need backporting. Usually the case.

I don't see "several", I just see one. Most of the non-simd benchmarks have almost exactly the same numbers for Rust and C. Perhaps the Rust test for fannkuch isn't optimized yet (looks like the C one has some extra logic about how to split up the chunks, whereas Rust blindly parallelizes)? I already optimized one Rust program, I'm not going to sit and optimize every benchmark out there -- we have tons of counterexamples of fast benchmarks already. It seems like you won't agree as long as one nonoptimized benchmark exists. In that case, good day to you. I'm done here.