Dude, just cutting out the resonator on an SVT is going to cause crazy drone - At first, you'll like it (like I did), but after awhile, it's going to drive you crazy and you'll end up replacing the straight pipe with something to quiet it down.. Search the archives and you'll find countless cases of this.. I've warned enough people, but no one seems to listen, but all eventually will put a resonator back in, because it makes long drives pretty annoying.
I myself haven't heard the car w/o mufflers, but I'm guessing it can't be too bad, as they're pretty straight-through mufflers to begin with, so I doubt they do much of a muffling job.. If you're looking for extra power though, you're looking in the wrong place, even an aftermarket cat-back is only going to give you 7-8hp tops..
