Which is better for mileage, tall or short tire?

[MrGoodpliers]

I recently pulled the 18s off my 72 suburban in favor of rallys for ride quality, towing a camper, etc. The tires I have on 8 inch rallys right now are 245/60 front and 255/70 rear. We just took a trip to the Smokies and with the burb loaded down with coolers, firewood, camping gear and the family, towing a pop-up we got over 16 mpg. I was pleasantly surprised. Now my question- I recently had some 9 inch rallys made for the rear and I was wondering if a taller tire would give me better mileage. I could use the 245/60s on the front and a 265/60 or 275/60 onthe rear--- or use the 255/70s on the front and a 275/70 or 285/70 on the rear. What do ya'll think?