https://cimg8.ibsrv.net/gimg/www.die...5a88f789ef.gif

https://cimg1.ibsrv.net/gimg/www.die...ced0e6fc3a.gif
chart to help you decide tire heoght and axle ratio for fuel milage

My 2007 G-56 has the lower ratio final drive that yields super high rpms at freeway speed.
To get a 35" approx tire diameter in a 17" I'd have to go 35-12.50-17's. I may have to go with an 18" rim and 285/295-75-18. I'd like to keep the narrower tread width. Problem is getting an 18" wheel in an appropriate backspacing so they're not sticking out.

Interesting charts, however it is all relative. Are these charts based upon traveling at 60mph on county roads, or 70-80MPH on the freeway?

Engines are generally the most efficient at their peak torque RPM, so if you cruise at that specific RPM you should get your best economy. If your engine does not have enough torque to cruise at the speed reached with your gear ratio at that RPM, you will have to down shift and lose economy. Also, if the engine is struggling to maintain peak torque RPM, parts of the engine will likely fail early due to excessive heat generated or excessive vibration.