Re: any? use cases. While dramatic speedup is not too common, MyHDL, a hardware description and verification language written in Python, is known to run 10 times faster on PyPy.
I also remark that MyHDL's simulation is competitive (on PyPy) with open source Icarus Verilog, in case you wonder why would anyone write HDL in Python.
Because Python isn't about performance.
Because it's not really 6.3 times faster for most(any?) use cases.
Because VMs are misunderstood as superfluous abstractions where a good interpreter should be instead.
Because VMs are understood as superfluous abstractions where a good OS should be instead.
...
And most of all, because better hardware costs less then the extra man hours involved the transition.