Well, I'm was talking about my firmware. The limit for the 6560 driver chips is 15 kHz and that is achievable if you do not need the kind of motion control that I use with my EazyCNC and G-code. I'm not 'pushing' this for RepRap, but just mentioning that as a possibility, it is a nice board, though I said it myself, and even if used just as a break out board for B6560AHQ, it could be useful.
br Kusti
br Kusti