Those are good points about string processing (and I wasn't aware of them, thanks!), but when I said Nim programs typically run a little faster I didn't mean on

Those are good points about string processing (and I wasn't aware of them, thanks!), but when I said Nim programs typically run a little faster I didn't mean only text munging, also my Project Euler type code: lots of loops, arrays randomly accessed and integer arithmetic. For those numeric programs the difference is pretty small, so maybe it's just the same slight edge that GCC sometimes has on Clang. (I guess I could try installing Clang, recompiling the Nim programs with Clang instead and checking if that brings their performance closer to the Rust ones.)