Hey Dennis,
My mate has an SSV ute with similar mods to your commodore and also a slightly lower diff ratio than standard (his put out around 330rwkw). My GTR currently puts out 250rwkw with more boost, computer, exhaust and injectors and would struggle to keep up in a straight line with the ute (especially if he gets traction). The ute is a very fun car to take a ride to say the least!
Have fun with the GTR, I think it is safe to say when you do upgrade turbos etc it just may blow the door handles off the commodore