Our friends down under at LS1 Turbo have ultimate performance mods for your 21st century GTO.
Excerpting from their site:
GEN-TT VE SUPER DUTY ENGINE DYNO
For those that want up to 1000hp of grunt from their G8/VE Gen-TT system we can now offer the 'Super Duty' system. Featuring large 500hp+ turbochargers and a higher flowing front mount intercooler the Super Duty system can supply enough air to satisfy even a 427 cubic inch engine. here in action at SAMS Performance in Sydney, Gen-TT Super Duty is pushing only 11psi of boost pressure into a low compression 427 to produce a genuine 920hp of grunt and over 800ftlb of tyre shredding torque at no more than 3500rpm. An awesome combination for the hardcore power hungry enthusiast.