166MHz 604e Card Info
These cards have a 48MHz oscillator that gives a 166MHz machine through a 3.5x multiplier, so the bus is running at 48MHz, and that leaves a small area to work with since bus maxes are around 55-60MHz these days. I have not yet clock chipped a 166MHz card, but I would expect them to max out around 180-195MHz. Here too, the L2 cache may be an important factor to keep in mind as some of the slower cache cards cannot be accelerated very far. So replacing the 48MHz oscillator with a 50MHz oscillator gives a 175MHz card, and a 55MHz oscillator would give a 192.5MHz card. Mod 1 and Mod 2 are the best ways to clock chip these machines since the initial oscillators are the metal can type. I've heard a report of 192.5MHz working just fine.
I've also heard a report of a 54MHz bus and a 4x bus:processor ratio to give a 216MHz processor that was stable.