Unity currently has quite a few Physics options, namely: Unity.Physics, Havok Physics, PhysX, and Box2D. This project here does some simple (sphere drop) stress tests for all four Physics backends. Feel free try out the repo yourself, or refer to a demo video below.
https://www.youtube.com/watch?v=rcJ6r16fWAA
Hardware for demo: Intel Core i7-7700K @ 4.20GHz; NVIDIA GeForce GTX 1080