I have the stage 1 pipes with no baffles in and a G56 air cleaner. With the standard set up I used to hit the top of the torque curve about 4250rpm and from then on it was a waste of time pushing it any further. But now it's 5250 before it flattens off and is noticeably quicker through the gears.
So much so I found myself topping the ton the other day without trying too hard.
