At work, I use PyPy to run a Luigi server for our data pipeline. It gave us a pretty dramatic decrease in latency and allowed us to scale our workload with a trivial change. It's unfortunate you can't choose your interpreter, but when you can it's pretty easy to just test both and see which one is faster.
I also use it at home to solve Project Euler problems. For anything that takes more than half a second or so, it's usually a big win and can turn minutes into seconds.