Agreed, but if we looked at the fitness of a Murray/Nadal/DJ/Hewitt, it's not really that far fetched.
Don't think DelPo can run a mile under highest 5's. Nor would Monfils be inclinded to try that hard. Querrey would die, and Isner barely hanging in there at low 6's.
Can Ferrer run it less than lowest 5's?