The normal GT3 MK1 have 350-354 PS at the flywheel.
I have PSI 3.8 litre motor with 450 PS
First I put the Cargraphic exhoust system (complete) with RS ECU and than it have 364 PS. After that I do the engine conversion to 3.8 litre with Cargraphic exhoust and it have 410 PS (lost about 20 PS with that exhoust), after that I put the heads from GT3 MK2 and PSI exhoust and than dyno showed 450 PS.