Headers on the 03/04 don't provide a lot of gain unless you've got a big twin screw pushin' lots of boost. Just the mid-pipe and cat-back addition though will get you 30-40 RWHP. You're lucky living in Mobile, you have one of the countries "Premier" 03/04 Cobra tuners right there in town.
If you take 15 minutes and read the FAQ at the top of the forum your question and maybe many others can and will be answered.
Yeah uncle meat, who is the tuner in Mobile? I'm moving to southern Tennessee soon and will be needing to find a new shop to tune my car now and then. I know Bennett Racing in Haleyvillle builds some nice engines, but don't know if they offer tuning.
James & Ed at RWTD (Running With The Devil) http://www.runninwiththedevil.com They utilize both Diablosport (Predator) and SCT (xCal 2) programming, your choice. James has been tuning 03/04 Cobra's & Lightning's for a long time and he really knows his chit! He has a full garage and dyno facility right there in Mobile.
honestly, your choice on exhaust should really be based on personal preference on the sound you like as well as budget. They'll all make similar power. The main difference will be in the sound. Some like loud and mean and some like the quiet sleeper type.
The thing I find with the Bassani is that it is a nice subdued sound at idle and normal drive conditions, but then you crack it open and people start jumping.