I'm perfectly fine with using 87 octane in vehicles that can't really take advantage of higher octane as long as it is a high quality fuel brand, with a top-tier brand my preferred fill (usually Shell or Chevron).
http://www.toptiergas.com/retailers.html
Gulf is definitely a blast from the past for me. Haven't seen a Gulf station in Florida since the late 80's or early 90's. They just didn't do well here.
High traffic stations help with obtaining fresh fuel too as PonySHO mentioned but sometimes you really don't have a choice, especially if the car is run until you absolutely have to get some gas. We use 87 all the time in my wife's '08 Honda Odyssey although I'll probably give 89 a shot at some point as it sometimes improves mileage in some vehicles, although the Odyssey gets pretty decent mileage for a minivan with 87.
However when it comes to any vehicles ($40K or otherwise) where premium is recommend let alone required and/or a performance oriented vehicle I take no chances and like knowing I'm getting all the performance I paid for out of the car as well as making sure the engine runs smoothly and cleanly. Especially with the SHO being DI, running turbos, AND high compression, high quality 93 is all I'll ever use, any unforeseable emergencies excepted of course.
Funny enough the car I just sold in order to get the SHO was a 2006 Subaru Impreza STI (awesome car!) and while the manual did say that you can temporarily use 87 if necessary with reduced performance, it really recomended/required 91 minimum with 93 preferred. Not sure how exactly the SHO manual reads as mine is scheduled for delivery May 5th.
I hope the stalling thing gets resolved for you with the fuel additive.
