Not sure on that one - I'm sure some of the GC8 boys will be able to give you the heads up on that one, although i haven't seen many GC8's re-mapping the OE-
ECU around here, so i suspect an aftermarket
ECU will be required to ensure it's all tuned up correctly.
It might be running alright on the stock
ECU but a good tune will not only ensure safety to the motor but also make it so that it's not a big hit of boost and then it falls down towards the redline which it what tends to happen on untuned cars with mods with no tune.
A tune will smooth it all out so you're getting max power all the way through while running at a safe AFR. I'd expect around 180/200awkw on a 34 tuned up on a 205 around 18-20psi.