I'd upgrade the injectors. In Calgary, Stage 2 is fine, but near sea level, a Stage 2 STi will be maxing out the stock injectors. Upgrading the turbo will push it far past that. If your tuner isn't even using all the fuel the stock injectors can provide, I feel like he's not anywhere close to what the car can do.
I upgraded my VF39 to an HTA68 and went with the 740cc injectors, and they worked great. If you're willing, a topfeed conversion would be ideal, as it opens up the options for injectors, but if you're already sitting ont he 740cc, use em.