@Apu So some results:
My warlock was level 22 on Friday night when I started leveling him up just 'cause. He's 92 as of this morning.
His last quest was somewhere in Tanaris, he still wears level 40ish gear - at some point I realized it was stupid queuing for 5-mans when I could do invasions instead. He's never even stepped foot in Outlands, Pandaria or Northrend (I need to go get some flight paths at some point though!).
If I'm invested in it a level takes about 10 minutes past 60. What I do is farm the same invasion by relogging after phase 2 until it has about 15 minutes to finish, then I actually do it all the way for the chest. making sure to kill the bosses in phase 3 since they give massive XP when they die (but don't be dead when they do or you get nothing, just tag and stay way back if needed).
The plan is to hit 100 tonight then open about, dunno, a zillion chests to fully gear up to 700+ in about a minute after.