If you still aren't satisfied with the power of your G60, look into having the head ported and polished (including a three angle valve job). Techtonics does this better than anybody else, If you can get them to do it. You'll be amazed at the improvement at higher rpm.
Since you'll have to replace the head bolts (stretch bolts aren't reusable), you might as well buy a set of super-strong RaceWear or ARP head bolts studs. The 16V motors need these too, they have a history of head gasket problems.
One of the two cars was treated to a cam designed for a GTI 8V engine. It did pull harder at high rpm, but our current thinking is the G60 should be optimized for maximum power between 4000 and 6000 rpm. Above that, the supercharger system just doesn't seem to be very efficient. In fact, although seat of the pants might try to tell you otherwise, drag racing the 2 cars (one with stock pulley, one with high-boost pulley) revealed very little difference at high rpm. I noticed no difference in the top speed, and quarter mile speed was only 2 mph better with the high boost pulley (but part throttle in everyday driving felt much faster. How can this be when there is a full 6 psi difference in boost at maximum rpm?
You must remember that heat is the enemy of power, increased heat means less power, and more spark knock, which triggers the knock sensor to retard timing. The result; even less power. The stock intercooler is far too small for optimum high boost operation, but there's no room for a larger one. And, as is true for most superchargers, it takes quite a bit of horsepower to spin the G60 to 15,000 rpm and 15 psi of boost, while turbos get high rpm nearly free, only at the expenses of increases in backpressure.
The G60 is an excellent car for general spirited driving, but try to make it a race engine and it fights you every step of the way. Low speed and midrange torque it does have (more so than even the VR6), and it's great acceleration in fourth or fifth gear on the highway is formidable. Let's face it, intercoolers work lots better in a 100 mph wind.
I managed to improve the "stock pulley" Corrado from 16.5 sec in the quarter mile to under 15.5 sec without ever going into the motor, but drag racing hardly tells the whole story. In a fifth gear low rpm test from 25-80 mph, the G60 car with the stock pulley beat a stock VR6 by almost 9 seconds, and many 5.0 Mustangs have fallen by the wayside once speeds climb over 100 mph.
The G60 will never have the spirited, quick revving feel of the VR6, but it has it's place too. It can out handle and out brake the VR6, and bought used; costs a lot less. Not to mention fuel economy. Some will fall in love with it if it's running the way it was intended. All can enjoy the G60 when it's properly maintained. And when the G60 is properly tuned, perhaps massaged a bit, well, even the VR6 owners will have to think twice before taking you on. Of course they'll be at the filling station while you're still out on the highway. We all know that positive manifold pressure is the way to nirvana.