Are you a manual or an auto? I would think you are going to have serious trans problems in the future if you are an auto. It is going to put alot of stress and load on the tranny, heating it up quickly and excessively. A manual you could get away with it, but be prepared to replace the clutch sooner than later.
As well gas millage is not exclusively due to RPM's. It is where the engine is most efficient.