When I was stage 2+ I never felt a difference between the 91 tune running 91 and the 93 tune running 94. I travel a lot and have used pretty much every gas station Ive seen around, aside from the one-off single location places. Ive used Pioneer, Husky, Ultramar, etc. Ive only ever had a problem with one single tank recently from the Shell across the street from my apartment building, where I always get gas from whenever I fill at home. Made my exhaust reek of sulfur smell and made a CEL come on twice. Two tanks of 94 then I started using that Shells 91 again and all was fine. No smell anymore and the CEL went off and stayed off so far. No one gas station or company will have the highest quality gas ALL the time. Theres always that one bad batch, like what I must have got.
If you want the peace of mind and you think 94 will be super duper for your car then limit yourself to finding only 94 octane gas. Id personally only search for it out of my normal driving routes if I was tuned for 93 again. My opinion is this car was designed to run on 91. 91 octane is 91 octane, I wont look for one company in particular to get it from, as its all the same to me. I just wont go to any of those one location places because of the horror stories I have heard from friends and family about places dumping water in their fuel to dilute it.