Don't wish to pour water on anyone's bonfire, but the debate should not revolve around multipe engine failures over water. Twins are safer, because if you get close to killing yourself in one, you've got loads of thrust to escape with (eg CFIT, microburst), when all engines are operating. In these circumstances, the four-engined aircraft loses because its excess thrust is minimal. Aircraft are lost, not because of multiple engine failures, but because of other, avoidable, situations, which are best escaped in a twin.