I went with the FR shorty header. I have an ATX and yes it made a diference but I have the full exhaust, intake and TB which contribute to the overall performance increase.
So, racing header only........not sure how much gain you would feel/get. I would have to believe there would be some just by eliminating the OEM cat but with stock exhaust?????????????. As far as it being a daily driver I wouldn't think that would make a difference so long as you could deal with the increased exhaust noise/tone.
Depending on your budget, I believe I would do something other than just throwing on a race header......like maybe start with an intake, UDP and cat back or maybe concentrate on exhaust only and do the header + cat-back. I did the cat-back first, then intake, then header,hi-flo cat (not needed for race header) flex, then TB but everyone has their own ideas.