even running the 4?10 keeping the rpm down shouldn;t kill the mpg, seeing 14 would be good, I'm usually down to mid 13 now, hand calulated and calculating the larger diameter tires as well, I really only saw a 1mpg drop with the bigger tires but it dropped my rpm a ton, 2000 was pushing 64 mph before, now I can comfortably run 67-69 18-1900 rpm
i did see a 11.34 mpg never getting over 70 mph not sure what is up there, it used to do better