Bigger sneakers
I am in the process of doing the same (once I can be sure the Abbotts or Truspeed unit will work) to lower road rpms. BUT - I realize I may be trading some torque and acceleration too. As to better mileage - Mebbe, that gets into volumetric efficiency, torque and Hp curves and all the great stuff in an excellent article in the TDR (issue 29??) and revisited just last issue. Bigger sneakers would tend to be more rotating mass (more fuel) and dropping rpm's too low would cause a performance hit (more fuel). I am aiming for 1800 at ~65 mph. With my 410's that's currently 2100 at 65.