GC aside, I've inspected assembly code (.wast files) for top 10 hottest methods in my code, and it was pretty much perfect, Rust and C will probably end up with something similar. However, there was no performance improvements whatsoever, those methods performed similarly to their JS equivalents.

UPD: modern JS engines are extremely capable of optimizing stuff and they can probably come up with machine code similar to what Rust or C will produce given that you keep your code predictable and optimization-friendly.