you are comparing apples to oranges.
i have the extreme on my 5.3. great sounds, loud, pretty mean sounding. has some drone, but not much (with cats)
my older brother has teh vortex on my 6.0. it is a very mellow sounding muffler, not really all that loud. his has some drone as well, less then my extreme however. the vortex does not sound nearly as agressive as the extreme.