I have been reading through the previous posts for the past hour now looking for the answer to this question. I am looking to put on a single stack 7" and I will need a muffler to reduce drone. Most guys seem quite happy with the 51" Donaldson from what I have read. The question is which one, I have heard guys running the M090544, M120100, and others. I think the 090544 is the 4" in/out which is what I would need, but is it the one best suited to reduce the drone? Also I have my cat in place...is it a true 51" will it fit between the cat and elbow for the stack on an extended cab truck?

So the short version...which Donaldson for an extended cab, 4" exhaust, cat in place, going to 7" stack? I regularly tow a 10K+ trailer with my wife and kids and I don't want to drive everyone crazy with drone.

Thanks!