Yesterday I managed to get my Pentium 166 MMX (black and silver chip) to 266mhz with a 75x3.5 multi and 2.9v (instead of 2.😎.

I used a 128mb cl2 pc133 chip (will only recognize 32mb for some reason).

The board I used is a QDI P5I430vx/250DM explorer II Speedeasy motherboard rev 3.0 PCB. Updated the bios to v 3.5s, which enabled jumper emulation and allows full control of the jumper settings in bios. This worked a treat and is probably the best boar I've ever used for OCing P1 chips.