I have had the flow FX for about 4 months and just did the B2Fab resonator delete. All i can say is....holy hell.... I would estimate it got between 50-75% louder when on the gas hard. Still fairly quiet putting around easy, more rumble at idle/parking lot speeds, but when you step on it...it actually gets pretty darn loud. I would consider the flow Fx by itself a "quiet" option, deleting the resonators made it "medium" loud. I'm actually amazed how much louder it got, i think its every bit as much of a change as going from stock to flow FX. Needless to say I love it, and I actually think the MDS got less noticeable somehow. But if you like the Flow FX being quiet... deleting the resonators put mine fairly into the "noticeably loud" category.
I always thought the Flow FX sounded good just quiet, after resonator delete I can actually hear the sound coming out behind the truck, before it was just kind of this muted sound in the middle of the truck. You can tell you're pumping out some volume behind the truck now.