I think even a slow card will work in the camera . The buffer will store data and load the card at what ever rate it can write . Sure there could be a delay when the buffer is full as it writes . I'm sure the spec is something I will never hit ( 4 fps for 10 seconds ) .
For my mind set, it's a medium format camera in a 35 mm housing . So a lot of tripod shots and live view , not much rapid fire street photography .