I want to help the exhaust breathe some but I don't want the added noise. So whats louder. The cat will ba staying. Straight pipe or 4 inch with high flow muffler?

I would bet straight pipe. The cat quiets things down a ton.

Just installed mbrp cat back system with muffler last week. I can barely hear the difference driveng down the road. It has a good deep tone though. It does seem to be getting slightly louder with milage, I don't know if the packing gets burned out or not, but it does seem to be ever so slightly louder than the first day of the install. I would recomend this system.

Take the cat off man

you will really get some serious sound then

I'm not looking for sound. Just want the extra flow with removing the muffler without getting it loud.