I went with 4.56's and just did a 100 mile round trip to the airport and back. Topped off the tank before I left, topped it off when I got back. 4.1 gallons to go 98 miles. I drove pretty much 70mph the whole way (2,600 rpm)
I have not tested it enough to notice a difference with city driving. But, I can now drive in 5th gear cruising at 45mph where before it would just bog with the 3.55's
I still haven't been able to control my right foot with it so I am pretty sure I could have done even better than the 23.9 mpg on the recent trip.
If you plan on staying N/A, 4.56's seem to be perfect!