Depending on the lender, one could argue that you would need to hit 780 before getting the most premier rates. But I agree in concept, an 840 doesn't really get you anything better than what a 790 score would, other than bragging rights, really. But a lot of us like to brag sometimes, including me.
Having a FICO score well into the 800's allows you to remain in a position to get the best rates even if you open a new account or 2. Also for employment that looks at your credit report, it can make a difference in how they perceive you, fair or not. It can also give you some power in buying a home or car.
The very same actions that helped me get very high scores, now makes me not be able to get a lot of CLI's. Recently tried to get a CLI on Cap1, they refused due to the fact I was only using a very small fraction of existing credit line. PIF every month and keep utilization very low and your score will soar, but issuers know they will make almost nothing from transactors, and they are not interested in raising your limit more just to boost your already high credit score. On personal loans, auto loans, and mortgages the high score is great, but don't expect constant CLI's on the cards you are never going over 15% utilization on, and never paying credit card issuers any interest. The issuers would love it if us high scoring transactors would just close our cards, to free up our credit limits for Revolvers who will pay them interest all year. They actually call us transactors...Deadbeats!!! Only in the banking circles would the most responsible debtors be called that.