Safin definitely - he's had two full days off, that's enough recovery time no matter how many hours someone's played in their previous matches.
But Hewitt I'm not so sure about. His match aginst Roddick may have been shorter than the previous two, which were 8 hours combined, but still lasted nearly three hours.
This factor, as well as Safin's greater power of the ground, is why I'm expecting a Safin victory in either three or four sets. However, Hewitt has defied my expectations in his previous three matches.