There's some payback calculation on 89 v. 87 octane and I can't remember exactly what it is. I'm thinking it's around 15 cents. Basically, if you have to pay more than 15 cents it's not worth it. Years ago there was a long thread about this and some chemical/fuel engineer had it all calculated out. Of course, this is all predicated on the fact that the engine is tuned/capable of using the higher octane which I believe these modern Rams are.
I had a longstanding argument with my dad about this. He swore up and down that putting 92 octane gas into his 1991 Toyota Camry was why the car lasted to nearly 300K miles. That engine wouldn't know the difference in the octane and he was ******* away my inheritance
It lasted to 300K miles because it was a Toyota.
Once a year I camp out in the sticks and the only gas available is ethanol-free 92 and my truck LOVES that stuff. I'm thinking I get 5-10% better mileage but that's because it has no ethanol.
The same engineer I cited above laughed about the whole ethanol in fuel thing and said after years in the industry the only reason he could figure we put 10% ethanol in the fuel is to keep the corn farmers in business. It causes autos to get 10% worse fuel mileage so it's kind of a wash.