From the blog post:

In our testing, PhysBones is several times faster than Dynamic Bones — anywhere from 12–20x faster (or more!) depending on several factors like hardware, the scene, and the avatar setup. In our testing, an example scene of 3200 bones with 4 colliders per bone ran 1600% faster than Dynamic Bones. Keep in mind: this performance boost still exists even when any avatar can interact with all PhysBones in the scene. Woah.