Hm, accordning to http://www.raspberrypi.org/forums/viewtopic.php?p=309582 it is possible to extend the amount of maximum sent data of the SPI bus! This is most interesting. This means I should be able to transfer a full framebuffer in one single transfer. Using 352×288 i might be able to do a full frame 30Hz update. If I succeed in increasing the SPI reception in the FPGA to 60Mbit I, in theory, can reach 60Hz.
This is not what it was intended for, but…. Still good to have some power in the SPI.