I have not seen one of these cards yet, but they have a 46.6MHz oscillator, and with a 5x multiplier that gives a 233MHz machine. With a 46.6MHz bus, that leaves a good amount of area to work with since bus maxes are around 60MHz these days. So, for example, replacing the 46.6MHz oscillator with a 50MHz oscillator gives you a 250MHz card, and that's a good starting point. Mod 1 and Mod 2 are the best ways to clock chip these machines since the initial oscillators are the metal can type.