Although the 640x480 is specifically for MaritzCX. There is no reason why not use that size for the other MSCs. It tends to be a more convenient size photo. After-all, MSCs have equipment to enlarge (640x480) quite comfortable.
I have yet to have a 640x480 photo rejected by any MSCs. One MSC sent me a corner of a 640x480 photo I had taken, which was a representative of there enlargement practices. 640x480 all the way, even when it is a business card only