I say yes... you are looking at a 30-35hp increase for a full system. They are pricey to begin with, and may be difficult to install on your own. If you got the bread, have a tech install them for you. IMHO, the exhaust is one of the very few areas Ford Engineers left on the table for a bit more improvement(OEM Tri-Y headers are very good, though)... skip the air box and throttle body!
Depending on which manufacturer you go with and want to keep it 49-state legal, it can be installed without requiring a tune and not throw any codes.
Kooks headers in 1-5/8" or 1-3/4" for stock to minimal bolt-ons. 1-7/8" or 2" for forced induction and very high horsepower levels.
Going with Kooks Headers with 1-5/8" primaries and Ultra High Flow(GESI) Catted X-Pipe... already have their Cat-back exhaust system. I have no plans or desires for an intake manifold swap, internal engine changes, or forced induction. I'll try to post before-after numbers when they are done next month.
2011 Mustang GT Premium 401A Spec- Sterling Gray, aka "Graycie", 6-Speed MT, 3.73, Brembo Brake Package, Current Mods: FRPP-Brakelines/Brake Ducts/Alternator/Radiator/Oil Pan/Oil Cooler/Trans.Scoop/Alum.Axle Cover, Steeda-Sport Springs/3rd Link/Adj.UCA/Alum.LCA/Rel.Brackets/Adj.PHB & Brace/Adj.F&R Swaybars/Adj.Front Endlinks/HD Strut Mounts/X11 Ball Joint/Bumpsteer/CAI, Koni Sport Shocks, ATI Damper, MGW Shifter, Kooks Catback, Wavetrac Diff, Michelin Pilot Super Sport... 93 Octane Performance Tune by VMP