87 octane is book recommendation (2013 CT). In high altitudes (Colorado) lower octane is sold as the "regular". For example, 85 octane is the lowest in the mountains here (Montrose, CO). This is because with higher elevation, there is less oxygen getting into the engine, and it is even harder to have premature ignition or detonation ("knock"). I manage aircraft engines, have built race-car engines, and am currently building a fully electronic engine system, which adjusts the timing like a car does, for an experimental aircraft. I have successfully made 1000 hp at the wheels (car) from a 2.0 liter engine. So this is with some consideration, research, and an undergraduate degree in chemistry that I will say the following:
Use "regular" gas wherever you are (lowest octane...usually 87). If the lowest octane is 86 or 85, use that. Lower octane fuel is slightly MORE explosive than higher octane numbers, and will possibly give you a slight bit more power per stroke, but certainly it will save you money. Your engine has knock sensors which will change the timing to protect the motor. Should you get 85 octane, for example (in high elevations)...then drive to sea-level and floor it, you might get some knock. You'll have to be pushing the engine to get knock, but likely could get significant knock in that case...particularly up a hill. If you manage to get significant knock (almost impossible in these engines with good fuel) you'll lose mileage and efficiency because the timing will be changed to eliminate the knock) this will give you less efficiency but protect the engine.
The detergent additives in "top-tier" gasolines are added after refineries produce the fuel. Chevron has Stoddard Solvent as part of their additive package. Others don't, from what I understand. All top-tier gasolines have additive packages, with "detergents" which are designed to keep the engine clean, particularly the fuel injectors. I have been told by a knowledgeable old-time race-car builder/racer that Chevron's "Techroline" additive is better than the others. I have my doubts, but don't know. I've been using top-tier gasolines mostly, but paying more attention to doing so now. I guess I'm finding that I'm wanting to go to Chevron more (because of this man's poisoning my brain), but I have a strong suspicion that Shell/Mobil are just as good with their solvent packages and that any top-tier gasoline (most of the big brands...you can look up a list, but they won't include your grocery store, Sam's Club, etc) will be equal.
Please comment if you happen to have any specific information on these additive packages.