The engine is built and tuned for 89 octane, anything more on a stock engine is a waste. ....But on a stock engine running 87 will decrease the power and put you all the closer to the limits of the knock sensor, a sensor that I wouldn't want to rely upon in the case of failure. Putting around town you are probably fine running 87 day in and day out, all you're towing is your ass. If you haul or tow any sort of load then I would run nothing less than 89 like is recommended.
That said, running less than 89 you are relying upon a sensor to detect knock and retard your timing thus reducing power output. If fuel economy is a big concern you probably shouldn't have bought a dodge for one, and secondly not one equiped with a Hemi. Sorta a waste to put around trying to squeeze every last drop.
I for one am happy to pay for premium(91 tune), enjoy the power available and tow like my truck was desgned for.
I have trailers to tow and loads to haul.