Dude, get a downpipe. That and the U-bend is the most restrictive part of the exhaust system. Your stock cat-back flows better than your stock downpipe. So basically you aftermarket mufflers are going to change the sound of your car, not the performance.

Do it right, get a downpipe. I recommend buying a bolt in section such as a 3" DP w/ 2.5" u-bend removal. Cat or Catless, your choice.