well, it was a good discussion I guess, but I would think this kind of driving would be really, really, rare.....even the autobaun has speed limits now....and no, the S/C wouldn't be disengaged...but fuel consumption is less than wot....it would only be hypothetical, but I would say you would probably drop 30% over normal fuel mileage, but again, it depends on the rpm running at that speed...I am usually busy hangin' on rather than watching what that is...lol