I went 1 to 75 in 4 RL days when I was sick over thanksgiving. I would have made 80 but I realized I hate northrend.
This was post 4.0 but pre-cata, on a nelfmage with weapon, shoulders, chest and trinket heirlooms, but no guild perks and no cloak.
I would imagine 85 wouldn't be that hard if you play 8 hours a day. Don't forget the inscription books for a shot at more bonus quest XP (or other stuff to speed your leveling)