These filters will give you more flow assuming there's not a greater restriction in your intake than the OE type filter.  I put one in a Sierra 1500 with a 4.8 which already had a 18 inch Magnaflow muffler.  I did notice a little smother/quicker response after dropping the filter in.  And could even swear it sounds a little better.  Downside is cleaning it.  You're better off to replace the filter as you run the risk of over oiling, or damaging it in a way that allows dirt through.  You'll never get it like new.  I recommend replacing every 25k or so if you want maximum performance & benefit without risk of dirtying up your mass flow sensor & intake.  So it is a bit costly.  That's why I give it a 4 rather than 5, I don't see it as a cleanable filter.