The FocusSport 5 Speed Zetec dyno sheet showed about a 3TQ/4HP gain on a car with I/H/E. I don't know what to expect on a 2.0L Duratec.
Keep in mind though, that power isn't the only thing that makes the difference. The car's whole attitude changes with a tune. Power delivery is smoother, the air, fuel, and ignition handling is refined, certain sensors and ECU parameters are re-calibrated, and the car simply feels different.
I would worry less about doing "pocket calculator dyno" numbers. The SCT unleashes the Focus' potential in more than just HP and TQ numbers.







So you wouldn't be able to dink around with a tune for my car. What about a custom?