Speed is not an issue for me. I currently have my 5D3 mirroring everything on my CF and SD cards. I understand that I can't do that with video because of the speed requirements of video record. Still, I can find anything in the menus to let me select the default storage location for videos. It mostly records on the SD card, but occasionally it has recorded videos on the CF card. I can't make much sense of it.
I would like to set it to default on the CF card because my SD card reader is much slower. Does anyone know how to set the record location for video when I am mirroring the storage for stills?