Hey cals granny,
Its colder here in Manitoba I bet. It's -41C here today with the windchill
The transfer vs. the cab may be 6 of one, 1/2 dozen of another. It doesn't hurt to ask when the transfer bus leaves. There may be another line for people getting regular cabs that could cause you to wait longer than the transfer.
The other thing that MAY cause some difference in you situation is you are on a larger ship with more people. I was commenting on my experience with Carnival on a smaller ship, with less people to disembark.
I can also say this. You say that your RCL ship will dock at 7am. Carnival was supposed to dock at 8am. The morning we got off Carnival Liberty, we were already docked, watching RCL's Oasis come in. So this could mean one or both of two things.
1.) Carnival Liberty docked earlier than what they claimed (8:00)
2.) RCL Oasis was late docking (7:00)
I think our ship was just extra early, but seems to be typical of Carnival. They say they will dock at 8:00, but many CCL customers in the past have commented on this forum that when they got out of bed, before 8:00 they were already docked.
I think you will still be fine, just take all the earliest options to get off as soon as you can, and look at the cab line and ask when the next bus transfer leaves and take the quickest option.
Another point here is that once you get to the point to make that decision, look at your watch. If it's 8:00, and your flight is 11:30, it's recomended to be at the airport for your flight, 60 or 90 minutes before departure? Well that means that based on the airline's recomendation, you're left with 2 full hours of travel time to get from port, to the airport. You could probably walk to the airport in 2 hours
I think you will be fine, but the larger group on Oasis or Allure, could slow you down. Best ask this in the RCL forum.