Depends on if you have any cpu-bound endpoints. At my previous employer we moved a very intensive check (high dimensional vector nearest neighbor search) into a separate Crystal microservice and even with RPC overhead it was easily 100x faster than the ruby version. This with code that any Ruby dev could instantly read, unlike if we would have gone for a C extension. That said, Ruby still has a massive lead in available gems, so don't uninstall Rails yet.

In my experiment, the Crystal version (https://github.com/nukata/little-scheme-in-crystal) was 38x faster than the Ruby version (https://github.com/nukata/little-scheme-in-ruby) and comparable to the Java version (https://github.com/nukata/little-scheme-in-java). Indeed, it is in the fastest group. See https://github.com/nukata/little-scheme#performance