First, octane ratings don't keep injectors clean. Additives do.
Second, gas is gas. The only difference in the brands is additives.
In fact, you're probably buying Chevron gas at Exxon and Valero gas at Wal-Mart. There are only three major pipelines coming out of the Houston-New Orleans region supplying fuel to the lower 48. Refineries pump in fuel but don't necessarily take theirs out. If Exxon puts in 10 million gallons on Monday they are allowed to take out 10 million the same day, even though what they put in is still only a couple of miles up the line. Exxon may pull out BP fuel, Valero may pull out Exxon fuel, and Chevron may pull out Shell. The fuel, regardless of who's it is, is then mixed off site with that companies additives. Gas is gas. Additives are the only difference.
Now consider that there are some 40 different blends of gasoline depending on which part of the country it is to be used and what time of year it is. You guys in CA are buring a different fuel then the guys in NE. Summer blends, winter blends, regional blends, and ethanol blends can make for comparing apples to oranges. What works in TX may not work in AZ.