I have an '07 SE, not Off-Road. I am ordering the skids (or trying to) and am waiting for Bilsten to come out with replacement shocks, but that is all I miss versus the Off-Road.
I've never used anything but 87-octane regular in the NY/NJ/PA area, and I've towed a 5,000+ loaded travel trailer at highway speeds, in stop-and-go traffic, and up-and-down some relatively steep inclines, and I've never had a knock or ping. I might try Premium when I go out the Rocky Mountains in a few weeks to see if I get better performance and/or fuel economy going uphill. My guess is yes, but not much, to both.
I used to do a lot of consulting work for a regional gasoline/oil distributor. If it makes you feel good to buy mid-grade gas, than by all means spend the extra money. But mid-grade is a marketing tool designed to appeal to folks who think they are doing something good for their car (better than regular) without "wasting" money on premium.
Vehicles are designed to run on regular or premium. There is not enough of a difference between regular and mid-grade to make any noticeable difference in engine performance or fuel economy, particularly in light of the extra cost. If your vehicle pings, knocks or hesitates with regular gas, you are better off spending the money on a tune-up than paying the extra $.10-15/gallon on mid-grade.
Gas prices just went over $4.00/gal for regular in NJ. I'm now researching propane conversion kits.