With stock size, not much drop. You'll lose a little just because of the added weight and the added rolling resistance of an interlocked tread pattern. But in stock diameter it won't be much. I'd expect 0.5 MPG drop which is just several dollars per month at the gas pump.
Those tires wear well. I bought a set for my Jeep Liberty diesel back in '05 and the second owner of that Jeep said that at 90,000 miles he finally had to replace them. I had put them on at 10,000 or so. So that's about 80K that they lasted. wow!