Thanks for the question.
Right now, we only support 16MHz and 32MHz. This is primarily due to the fact that the we want the microcontroller IP to remain compatible with all of the existing libraries that are expecting a 16MHz clock. Handling the 2X speed is fairly straightforward, but other multipliers of the clock get tricky with a lot of libraries.
Would 32MHz work? Or do you need 20MHz or 22.1184MHz, specifically? Can you provide some additional details regarding how you want to use it?