I have a Rocket Chip Stage 2 tune with extra extra large fuel injection Nozzles, and driving around town in KC I can pull 42 MPG pretty easily - an all highway trip should get me 45+ MPG and >600 miles for the tank (I've actually pulled 735 miles for one tank - put darned close to 17 gallons in it !). O1m changed out to 5 speed manual at 252,000 miles (currently at 378,000 miles), and I can spin the tires in 1st and 2nd gears. I usually drive pretty sanely, and I can pull redline+ RPMs in at least 2nd (and probably 3rd and maybe 4th gears as well - I haven't taken it that fast).
Oh - I do have a ScanGuage 2 and on the guages - I use Avg MPG, Boost, water Temp (to makeup for lack of guage / idiot light) and MPH. If you coast downhill in gear, it's very easy to get to 50 MPG.