Power off the line did indeed suffer with the Nittos. It wasn't much, but the "butt-dyno" did register it.
Conversely, engine works less hard "at speed", as you are moving farther for every revolution of the bigger tires. I've found that the less efficient take-offs versus the more efficient cruising have cancelled each other out, as my overall around-town mileage didn't change with the new meats.
As for mileage, you actually get *better* mileage than your odo shows, as it too is about 7% too slow (I paced off 50 miles using highway markers, compared that to my odo reading, 6.9% off). I made the adjustment when I crunched those numbers to get 21 mpg.
I was wondering if the less "on the ground" torque with the bigger meats might actually make it handle better on ice/snow, since its less likely to break loose upon initial acceleration? Guess I'll have to wait for next year to put that to the test . . .

And of course, in the end, its all academic . . . mileage? We don't need no stinkin' mileage!

Ron