I had no rested at all.
And was 80th.

Did Vashj'ir with the Druids.
Ended up 81.92, so almost 82nd.
That was a single session of play, no stopping.

If you have any amount of rested...
Either of Hyjal/Vashj'ir will get you to 82nd.
Deepholme will get you to 83rd, unless you do the other 80-82 zone.
Uldum will get you to 84th (or almost 85th, if you did both 80-82 zones).
Twilight will ding you to 85th at some point.

If you have any PvP aspirations...
Consider capping your honor, I believe that's 5,000 honor.
Before 85th.
That will get you a few pieces of the PvP gear.
Being 5x 83's or 84's, will let you dominate the bracket.
A fresh set of 85's, is more than decent because of having five.
But leveling in the PvP is a break and change of pace; and leaves you more quests to do a max level for gold too.