These ones found no difference:
http://www.etalabs.net/compare_libcs.html
https://users.rust-lang.org/t/optimizing-rust-binaries-obser...
This guy found Musl much slower for multithreaded allocation:
https://www.linkedin.com/pulse/testing-alternative-c-memory-...
These found Musl a bit slower with LTO:
https://github.com/vectordotdev/vector/issues/2313
Except for that LinkedIn one (which feels like it might be a bug), it seems like there isn't really much in it, which is what I'd expect tbh. Kind of like Clang vs GCC. Sometimes one is faster, but probably not by much.