If you want to do it in style and not be just another mustang owner, go Grand National. Most fun for your $ and all bolt on power. Plus you get to enjoy the same limited production cool factor as your MM and I guarantee you'll not experience a more butt clenching ride than a hole shot in an Alky injected GN.
03 300A
Trilogy #154
Stainless Works LongTube Headers, Magnaflow High Flow Cats, X-Tube, Rear Cat Delete, Borla Mufflers, 2.5 Mandrel Bent pipes
Lido tune
Performance Transmission, 2500 Stall