Crowd level 7 is do-able. However, I have noted as a frequently visiting annual passholder that TP has been consistently off, several times two levels above prediction. I’ve been days when 7 was predicted and saw elbow to elbow crowds and wondered what happened, gone home and looked up the next day to find we were trudging through a 9.
Because December is not hot and humid, even a 9 is do-able if you have your FP and a good touring plan set in place, but I usually won’t go unless 6 or less is predicted. I’ve worn myself out on the level 7 and above crowds. I get tired of the cattle feeling when we’re loading on the monorail or the ferry. By the time I get to the park, I’ve had it, but that’s just because I’ve done it so many times, and I know I can come back on days when it’s not that crowded. But, hey, if this is your only opportunity to go, it’s much better to go in December than in the summer. Much better atmosphere and temperatures.
When I’m planning to go on a crowded day, I load my Fast Passes in the middle of the afternoon from 1 to 4 when the crowds are the worst. We get to the park early and ride our non-fast pass rides until 10:30 and then leave the park for an early lunch, come back do our afternoon Fast Passes, then have dinner and try to get in whatever we have the energy for after 4:30 with whatever Fast Passes are leftover or whatever has low wait times, but truthfully, on the high crowd days we’re ready to go by dinner time.