I agree with 411A on 50 feet being quite adequate for prevention of 'busting' the MDA. If you want hard proof (and runways are pretty hard), on the B777 we use 20 feet as the Cat IIIB minimum, and missed approaches from 20 feet are regularly achievable without runway contact.
That's for an automated Go-Around of course, add a further 30 feet 'fudge factor' for the human manipulated Go-Around, and 50 feet additive to the published MDA is quite adequate, I've seen it numerous times in the simulator without MDA 'busts'.
Regards,
Old Smokey