re CLI, the author of esbuild had an interesting comment about writing it in both Go and Rust and the Go version being faster out of the box https://news.ycombinator.com/item?id=22336284
GC gives you a nice cushion, because it makes allocations fast. However, with a little bit of thought put into memory allocation (such as using arenas with bump allocation), you'd easily beat Go with Rust. The author of SWC did exactly that https://swc.rs/docs/benchmarks