Boat US did a study, bolting cleats to steel plate and breaking them. Obviously, on a boat, this depends on a strong backing plate.
Different size cleats? In the case of fastener failures, simply adjust in proportion to the fasteners you have (data found here). In the case of feet failures, expect the strength to go up size^2. The strength of the foot, for example, probably goes up with size^3, but leverage goes up with size^1.