The specific example that comes to mind was translating a Java application doing similarity search on a large dataset into fairly naive Rust doing the same. Throughput I guess. It may be possible to optimize Rust to get there but it’s also possible to (and in this case did) end up with less understandable code that runs at 30% the speed.

Edit: And probably for that specific example it’d be best to go all the way to some optimized library like FAISS, so maybe C++ still wins?