Finding which turbo works well for your application is going to be the key.

Here is what I've found that works and I'm guessing get's pretty close to 300 flywheel horsepower.

The chips on the market can call for max fuel from the DS4 which can put down (if a very healthy pump that is) approximatly 80cc's of fuel at the MOST.

Which is enough, barely.

You're right, the GM-x turbo isn't going to get close.

Another key, this setup HAS to be used with a CHARGE AIR COOLER (aka intercooler).

J