Brian Cantrill has a video out there where he rewrote some C code in Rust and the benchmark was enough faster that he couldn't make sense of it. After much digging it turned out that it was because Rust was using a better data structure to represent the data, one that's difficult to get right in C.

In the end his test was comparing algorithms not compilers, but there is still something to that: we always make algorithmic compromises based on what is robust and what is brittle in our language of choice. The speed limits don't matter if only a madman would ever drive that fast.