And for my opinions.
The GT500s are awesome, and sound awesome. Nice burble on decel with a nice muscle car rumble when you are on it. Its a small step above stock, but not enough for me. They sound much better when paired with cat deletes or an offroad H. The offroad X will make them raspy and me no likey that.
The magnaflow muffler deletes are on the opposite side of the coin. They are totally straight through pipes with nice 4" tips on them. They make the car sound agressive and mean, but will allow you to keep the cats. So its the best of both worlds if you want both muscle car sound with loud volume but no stink and not illegal. Also you would need a tune to kill that CEL that will come on without cats. NOW, if you decide to pull the cats with the muffler deletes, they simply will be way too loud for the street. They are nascar loud with no cats in front of them. This is no bueno.
The stock exhaust with cat deletes sounds a little better than stock with almost no stink, but there is this tinney sound that comes from them when driving hard and its annoying as shit. I say forget that route if you want no cats. Just get the GT500s. They can be had from LMR for $300. Also the magnaflow muffler deletes can be had from planet magnaflow for like $390. You have to make them an offer from the page, and it will email you back with the lowest price. This goes the same for all magnaflow products from them. Magnaflow will not let anyone advertise lower than their vendor pricing or whatever.
So I got the GT500s for my new 5.0, but I think I want the muffler deletes again for now. I plan on keeping the cats for a while, but still want volume. And when Im ready for no cats, Ill throw my GT500's back on with them.