I sized up one full size but that is mainly because of my calfs, I have big calfs so I need the extra room in the shaft.
When they get marked down, they will get marked down at each Saks. Not sure if NM has them because I don't shop there, but BG has them but that is only one store. My recommendation is to get them a few days before Christmas, this way once they get marked down, you can just get a price adjustment. But confirm this with an SA so you don't end up paying full price.
That's what I do with all the purchases I make that are late in the season and I know are about to go on sale, if you wait until the actual sale or pre-sale starts, they will likely be all gone at that point.