If mileage is a concern, why put on wider/taller tires? I mean, if it's to be able to handle more weight when hauling/towing I get it, but otherwise you're not helping yourself with tires that large.

I don't bother tracking mileage in town because I just don't put enough miles on her to care, but my truck flirts with low 20s on long highway runs if I keep it under 75. Slightly different setup than yours, though, and I'm running the OE size 235/85/16 on mine. Might go 265/75/16 on the next set just for a better stance, but that'll probably be a few years off and more due to rot than mileage.

Mike