it'll all be based on the flow characteristics on the turbo, once you open everything up on the intake and exhaust sides. i would think it would be tapped out at around 300whp on GSR setup - and thats already pushing it.

unless you upgrade the internal wastegate to hold more than 12-14psi, you're going to have to deal with boost creep and other related issues.

the whole wastegate exit port and elbow off the exhaust side really hinders power potential.