Performance Upgrades?

Does anyone know of any aftermarket performance upgrades available for the CTS? My searches just come up with articles on the new CTS-V. And I am not wondering about exhaust or intake, I want big gains, 50-75+ HP. I also read that there is a european tuner for the CTS but it might just be for exterior mods.

as a small shot of nitrous.... easy and inexpensive....