I have the Flowmaster 40 on my V6, and I have to say that I'm a little disappointed in the sound. At idle and low RPM it sounds low and beefy (the MagnaFlow hi-flow cat actually made the sound even deeper). But once you goose the throttle, you experience the "fartcan" sound. I think you just can't get that big block 454 sound with a V6, you gotta sacrifice somewhere. However, the MagnaFlow (to my recollection) uses the glass-pack method, with gives the truck a deep, yet muffled sound. They can still be loud, but I think they give off a little more of a high-performance "tuned" sound than a Flowmaster.
Just my opinion though..... <img src="/forums/images/graemlins/kewl.gif" alt="" />