I've got a ScanGauge, and have calibrated the fuel economy feature. My mileage, with 1900 miles on the car, is a combined city and highway 24 mpg. If I go easy, I can get combined 26, but that means loafing up the twisties, which is very difficult to do. I don't have a good number yet for pure highway driving. My only mod is the MSCAI. Before I put the CAI on, I saw 28 mpg with mostly highway driving.
Since you're interested in performance and economy, I would highly recommend this car. I don't enjoy driving a slow car either......