You can run a lot more timing with headers or cat deletes on the car even at 550rwhp. Like about 6 degrees more at the same A/F with no detonation or worrying about cats melting. This is enough to make a nice hp gain after a retune even with running 1.5-2.0 psi less boost.even if you do loose some boost on the gauge, you still have the same power. You really dont gain much by this, unless you are modded more than the average car. Above 575-600whp, you would start to gain some real hp.