I have the 265/75-16 E-range BFG ATs on my 2005 Tacoma (4WD DC/LB). Mine are rated 80psi max and I run them at 80psi cold for on-pavement mileage. At that pressure I get almost the same mileage I got before with 3-ply 245/75-16 Bridgestones (measured by true GPS mileage, the 265s at 80psi read 3.48% low on the odometer), 18.5-20.5mpg. They ride stiff but not uncomfortably so, and they handle pretty decently.
Off pavement, I tend to go down to 40-50psi for good washboard roads. Lots more side-to-side flex in transitions and much better traction on loose stuff. Mileage drops another 1-2mpg at 45psi.
In hard stuff, 12-15psi and they're like tank treads. Really supple, flexible sidewalls. Haven't spun one on the rim at 12psi yet (stock wheels, not beadlocks), but I believe it does happen sometimes. One time I left them too low (~20psi) for too long and got a sidewall puncture when I picked up too much speed on hard, sharp rocks in Death Valley. It's nice to have such a broad range of usable pressures but it does mean stopping to use the compressor pretty often.
Wear: the tread is flat at about 50psi with my moderate loads (~5500 lbs net loaded). Poor shoulder contact at 80psi. I did the math and with my mileage vs. sale price on tires ($150ea), I save money by wearing out tires a little faster and getting better highway mileage. YMMV.
