If it's a standard unit, the turbo is at it's best at 1bar of boost. Much more boost than this will cause the turbo to become inefficient. I think it tops out at 1.2 bar (could be wrong here though), but if you want to run that (or more) than i recommend you go for an aftermarket GTiR turbo from someone like Turbo Dynamics.
They have 6 "stages" of turbo designed for the GTiR engine. Stages 3 to 6 are all roller bearing - for a much faster spool. The others all have different chamber sizes.