How I do it...

10-20 -> Wailing Caverns
20-38 -> Scarlet Monastery
38-48 -> Zul'Farrak
48-58 -> LBRS and the first room of UBRS.

With WC and SM you're going to get locked. I can usually get SM done in about 35 minutes. Really nice to get 4-6 levels in SM in 35 minutes, then relax for a bit. This is just how I do it with a weird schedule. It's a lot less running and with an epic flying mount and level 23 guild, really easy and not much movement required. I usually don't get a mount til level 38 when I do ZF. Mounts are pretty nice for ZF though.

One nice thing about LBRS is that there is a point in the instance where you can stand and get about 95% of the xp for the rest of the instance. When you get to the ogre part, there's a bridge. If you place your boosting characters halfway on the bridge, you'll get XP for the rest of the instance. You only have to move your slaves 3-4 times before this point and I was eventually getting to where I could do a LBRS run in about 20-30 minutes. I did it with an 83 Ret Paladin in Prot gear, so I'd imagine with a better geared level 80 it'd be quicker.

The reason why a geared level 80 is better because the stats at 80 are more ridiculous than at level 85. My level 81 Mage in 4 piece t10 has like 30% haste, 45% crit, and a little less spell power. You will do more dps in a t10 geared toon than a heroic geared level 85.

EDIT: I quest from 58+. I don't know why, i just find them easier, and honestly even though dungeoning is pretty OP, the quests in Outlands and Northrend are really enjoyable with RaF. I went from 59-63 on my mages in about 90-120 minutes. The first quests in Hellfire are a bitch though(Collect wood and bloods), but beyond that its kill kill kill.