What is the performance like for symbolic maths?

I always preferred Mathematica for that to SymPy since it's baked in to the language much more. It was also way way faster than SymPy was for anything interesting.

Performance is pretty good for most stuff by now. However, there are functions which not optimized yet or implemented in a very basic way and if you use them in non-trivial ways the performance might be quite slow. We're happy about any reports of such issues at https://github.com/ad-si/Woxi/issues!