Simple benchmarks are a useful yardstick. I recently wrote a service in Rust/Iron which only has 4.7x the throughput of the same Ruby/Rails service. That was rather disappointing considering how much more effort is required to do it in a lower level language.

Is Python/Django performance significantly worse than Ruby/Rails? The situations you describe are things I do every day in Ruby. Getting 1000 rows from the DB and performing some operation only takes a couple of milliseconds in Ruby.

Ruby/Python are meant to be glue, and you can most certainly use them to glue together "interesting things", like image processing or audio processing in a web layer.

Memory caching rarely changed, often accessed, but ultimately persisted in a DB things like exchange rates in a global object is exactly what you do in Rails. There's a specific helper for doing it. http://api.rubyonrails.org/classes/ActiveSupport/Cache/Memor...