With a catted pipe you
should still be able to pass emissions. Some people don't have to worry about it. Check your local laws. Some people only have a sniffer test, and can pass with a catless pipe. Others that have the visual too are screwed.
If you want to hear various exhaust combos, check out
www.mustangexhaust.com. Try to determine which sound you like best, because the power is going to be about the same.