If you are willing to leave that card for $40, you could tell them you plan switch to another card because you're unhappy with the rewards limit, and then cancel if they don't try to keep you by adding the $40.
There are many other cards on the market that don't cap rewards.
I've stuck with Citi mainly out of laziness. We were getting decent rewards and the 5% rolling categories worked out pretty well for us.
We've already moved on to a new credit card with similar rewards and no cap. After a few months of inactivity, we'll see if Citi loosens up and decides to give me the rewards that were over the limit. If not, then I guess I won't be using the Citi card again. Oh well...