I don't know about the CFM ratings, or anything else, but many of the guys I work with have decided to run straight pipes. I'm not big on that, so for the same price, I had a local muffler shop put in a glass-pack muffler. I do get a bit of drone (quite a bit when I'm pulling hard)--but I suspect that some of it will quiten down with a well-placed muffler hanger--I've determined most of what I hear in the cab is vibration rather than exaust note.
Outside, it's rather loud, but not as loud as a gasser with straights or even glass-packs... and my total cost was $65 installed.
Just something to consider--I have had a slight mileage improvement, but I won't attribute it specifically to a muffler, since I do work it so hard--but to the tune of around . 5 MPG under load... .
--Just my thoughts.
Chris