I haven't looked on Delta's site, but I know that not all airlines have a weight limit on their carryons.
That said, the weight limit IS however heavy the suitcase can be so that you can lift 3 carryons in a row over your head without hitting anyone, and then at the end of the flight gently and carefully take those 3 bags in a row DOWN without hitting anyone. DH still has a scar from a flight a few months ago, when a woman had packed her carryon too heavy, and she dropped it while taking it down. It landed on his leg and cut him rather deeply.
So that's always the true weight limit...light enough for you to not injure yourself or others (especially others) while putting bags and up and down.
Should you check a bag? Why not? Makes it a little bit easier to pack. Of course, if that bag is delayed, be sure you have bathings suits and a change of underoos (ha) for everyone, in the carryons.
But it did amuse me that you said you have small bags that fit the limit...the ONLY bags we have fit carryon size, and we consider them to be quite roomy! We rarely bring them onto the plane, they are generally our checked bags (b/c we unzip the extra zipper and stuff them so they don't meet carryon size by an inch or so), but still, they are very roomy even when we pack them to carry on board.
