As we allow know, the larger diameter tire will reduce rpm at cruising speed. Weight differ should be negligible. I would make sure you stay at the same width so you don't increase friction, get a LRR tire like the Ecopia EP100/Ep422, Energy Saver A/S, dB Super E-Spec or Nokian i3, etc. and ensure you register the speedometer difference so you don't mistake a mpg due to traveling slower/faster than you think you are.
