We did the same thing you are doing with 5 adults in a cabin on the Paradise. It was a bit cramped but we managed just fine. We booked a 6A guarantee and got put in a 6B. I have sailed on Carnival many times now and there is no difference in size between the outside cabins until you get up to the suites. The only diffence is how many floors you have to walk up.
Have a great time.