An interesting side bar to this discussion is that the Air Force has installed winglets on their B757's albeit they had not requsted this mod but the local political hacks in Washington state aked for them as part of a budget request. The winglets are built in Washington! At any rate because the 89th is not as concerned with fuel burns as opposed to schedule requirements, they frequently fly the aircraft at .83/.84 under ideal conditions. What they have found out is the winglet equipped aircraft actually burn more fuel then a comparable non-winglet aircraft at the same higher mach numbers. Obviously the winglets serve a useful purpose when flown in the more conservative airline mode as opposed to a max cruise speed curve.