How fast can ARM Cortex M0s/M3s bit bang?
If I read the SPIO0/1-with-SSP chapter correctly using the TISS format (fig 36 in my rev 12 copy of the user manual, link to newer version) can send out a continuous bit stream. The maximum clock rate seems to be PCLK / (CPSDVSRx(SCR+1)), for 48 MHz, CPSDVSR=2 (seems to be the minimum) and SCR=0 (default) this would give 24 MHz.

Were are you going to find the data to clock out at that speed? This poor chip (OK, it is my favorite!) has only 4K RAM and 32K FLASH.