The slowest Pentium Pro was (I think) 150MHz, with the fastest being (IIRC) 233MHz.The fastest PPro was 200MHz. Some boards would let you overclock them but I was never able to get mine stable at 233MHz.
Now is where it starts to get funny. The Pentium-II started at 166Mhz was a slightly-enhanced Pentium Pro with half-speed, off-chip cache in a Slot1 package.The PII started at 233MHz, had twice the L1 cache (32KB) of the PPro, and MMX.
It was almost identical to the Pentium Pro, so identical that you could at once time buy "Pentium Pro Overdrive" chips to put in your P6 sockets, chips that were more or less socketed versions of the P-II.You could also buy the converse - slots with socket-8 on them to put a PPro CPU in a PII board. Computernerd used to sell them. PPro 200 with 1MB on-chip L2 was tough to beat for a file server until PII went to a 100MHz FSB.