I'm certainly no expert in transatlantic cruises, but we have done two. Both were in September. On one of them, we ran into the end of a hurricane, and the seas were very high, plus strong winds. Couldn't go out on deck for a couple of days. The other TA crossing was as smooth as glass.
I'm not familiar with TA cruises that go in November/December - I thought most were in the September/October time frame (hurricane season in the Atlantic).
Whenever we cruise, we always book as far in advance as possible. First, to get the cabin we want, second, to get the best price. We know other folks who wait till the last minute. As they say, to each his own.
You should factor in the ports the ship will visit, especially if the cruise will stop at a place you really want to visit.
Others with more TA experience will most likely have something to add. Enjoy.