Here where I live the gas comes in one or two refineries it's just the additive that the company like shell or chevron add that's different. As long as it's top tier gas it sucks there's only 91 oct here in CA.
Talking about carbon fiber I just got the last pieces from Seibon. Going to the shop next Wednesday to get it properly installed as far as Fitment I'll let you guys know aside from that I rather have carbon fiber than chrome and some cars looks amazing with carbon fiber.
I have the hks and it sounds amazing in my opinion. it gets loud when I put on sports but not obnoxiously loud and it also depends if u have a stock, catted, or catless dp.