Stock size is 265/70/16. A nominal 31" diameter. I assume these trucks were sold with P-series "fake" all terrain tires. So...putting a real all terrain tire that is significantly heavier on the truck will put a small ding into your mileage and power.
The next size up is 265/75/16. This is a 1-inch greater diameter tire, so it gives you a 1/2 inch lift over stock. Most folks think it looks better, especially if you lift the truck 2". Visually, they seem to fill the wheel well better.
With these 32" tires you can expect a noticeable hit in power, acceleration, and gas mileage. Many here say it's worth it for the looks and slightly better ground clearance. Also, many here state that with 265/75/16 tires on a 2" lifted 4runner there is no issue with rubbing.
I chose to, even though my 4Runner has a 2"+ lift, to go with the stock size. I want to preserve the driving dynamics and mileage as closely as I can. With stock size tires and the 4R loaded with camping gear or passengers, I can just barely stay in 4th gear when ascending the big, long grades on the interstates. I got BFG AT/KO2 tires this time. I've been using BFG AT tires since 1998 across 4 different vehicles. They are extra expensive in the 265/70/16 size for no known reason.
I don't want to go back to the power level of my old 4 cylinder Toyota 4WD truck, which had to use 3rd gear on those long climbs. Never again!
Hope this helps.