I would guess the busiest travel day would be Sunday over Saturday. Chances of a sale during one of the busiest travel weeks of the year? Probably zero.
The Sunday after Thanksgiving is the busiest travel day of the year...whether you are driving or flying, it is going to be a headache. I would think that Saturday is going to be busy as well, but not as busy as Sunday.
We have flown out of ATL to MCO on the Sunday after Thanksgiving before but usually have an early AM flight. Usually people are leaving MCO that day and usually in the afternoon/evening times.
If you do decide on either day I would go for the early morning flights. And YES we have seen discounts but we always fly AirTran.