So I managed to get my last two alliance level 90's pushed through to 100 over the last couple of weeks - my shaman and my paladin. Both came in right at that 9 - 9 1/2 hour mark on played time which seems to be pretty consistent. Note that I'm not doing anything extraordinary to cheese these - just using garrison potions and full heirlooms. Their are clearly opportunities to level much faster than this using stacked bonus objectives and the huge xp boost potions. But I still enjoy the questing process, so this is basically just straight questing with some bonuses added in.
So with all of my previous max level toons now sitting at 100, I'm moving on to working through some lowbies. Rather than the previous approach that I've taken of leveling them each a bit at a time to maximize rested xp, I've decided I'm just going to bang them out one at a time, so that rather than having a bunch of toons stuck at some mid to high level but not max when the next expansion launches, I'll instead have several more hopefully sitting at 100. We'll see if I can get all of them there in that amount of time.
Next up is my alliance druid, who is currently at level 76 and working his way through Northrend. After that, I will probably do my alliance mage, just to leverage a shiny new heirloom ring I got from a shipyard mission.