I know mine's not a gts-t, but ive got well over 300rwKw on my gtr, and 550 injectors are fine, well i have a full fuelling system set up. Fuel consumption, i once did purely city driving n no highway, only got 270kms out of like 62L thereabouts, but i run a very rich tune. Tell your tuner how u want the tune to be, response or max output or etc. Dyno figures are not everything.