It would be possible to see a slight mileage gain with premium gas but it wouldn't have anything to do with the octane rating. At many stations the premium gas doesn't contain any ethanol so compared to the 87 octane with 10% ethanol there could be a slight increase in mpg. Probably barely noticeable and certainly not enough to offset the higher price of the premium. In another thread someone pointed out that it isn't automatic that premium doesn't have ethanol. If it isn't labeled on the pump as ethanol-free it probably isn't.
I like crawling under my cars. I like to get my hands dirty on the undercarriage. There is no better monitor than to get to know your car well enough to see the changes. Kinda like having kids.And the overpowered 3.6 owners get to crawl under their car to change oil filters. No wait, they don't want to get their hands dirty.
Where I live, all gasoline comes from the same set of tanks at the port. I'm in a 10% Ethanol state. The additive package really doesn't matter much since E10 is a perfectly good solvent to keep your injectors clean.From what I have heard all major gas (within octane rating) is the same, the difference is the detergent packet added when the tanker leaves the distribution supply yard. Apparently each Major runs a specific detergent which might do a specific job of "cleaning". Unfortunately, one cleaner might not be the only one your engine needs. It's suggested you vary the gas Brand you use occasionally.