Listen to Raj he loves statistics.....and is right. However, Dyno's and turbo's don't mix. Take the car to the track. Dyno's don't load turbo cars right and in my opinion your car's tune-up will be a little off and will make more than 600hp.
Only problem with your theory is that the car makes the same exact amount of boost whether its on the dyno or making a banzi run down the street.
Something else is up... I've got some other ideas, but when all is said and done I believe that this turbo may just be able to make more power on this combo.