I'm liking the agressive tone of the 40 series delta flow, but at the same time, I don't want to be hearing it too too much inside the truck. But I still want the nice loud agressive sound on the outside as I leave somewhere. I'm thinking the 40 Delta Flow is going to be the happy medium between the full-fledged 40 seres and the 40 super and a mellower and quieter 50 or 60 series.