My familiarity with PTP is in the context of distributed embedded systems, sometimes using the PTP hardware for relative synchronization without even having an absolute reference; but in that world, PTP precision is an order or magnitude or two better than "within 100 microseconds" -- 1 us is a sane target, and 5 us is very comfortable.
For what it’s worth, we normally aim for < 50 nanoseconds RMS on our systems with PTP. You can get even better if you combine it with synchronous Ethernet.
