1. Yes. It's different for different cars, but it usually robs a little low end, but really cranks in the high RPMs.. But if you get electric-cutouts you can change them as you drive.. So close from start, then open 'em up once your off.

2. When they are closed you can't even tell you have them. When you open, your exhaust will be WAYYYY louder than stock. Not sure about the crossfire, but on V-8s it'll make your ears bleed. like a harley riding by you. its sweet. :-D

3. Uhhhhh tough decision. Complete exhaust systems by Borla and such companies can create a big improvement with performance, but the cutouts don't have any defined results. SO if you just wanted the loud exhaust, yes shoulda got cutouts. for performance I'd say you made the right choice.