Demonbane

Initial impression is this racial doesn't hold a candle to Troll Beast Slaying as far as powerleveling applicability.

Here is a quick list of zones with a significant populations of demons if you are looking to take advantage of this passive while powerleveling a holy goat and happen to have found your way to this comment:

*Note: The Legion pre patch invasion event flooded Azshara, Dun Morogh, Hillsbrad Foothills, Northern Barrens, Tanaris and Westfall with tons of demons so most of the demon NPCs Wowhead has listed for these zones are legacy data no longer up on live servers.

Eastern Kingdoms
Blasted Lands (40-60)
Burning Steppes (40-60)

Kalimdor
Darkshore (10-60)
Ashenvale (15-60)
Desolace (tons!) (30-60)
Thousand Needles (40-60)
Felwood (tons!) (40-60)

Outland
Hellfire Peninsula (58-80)
Blade's Edge Mountains (65-80)
Netherstorm (67-80)
Shadowmoon Valley (67-80)

Northrend
Arthas apparently built an effective wall to keep out the demons (there's nearly none).

Cataclysm Zones
Mount Hyjal (80-90)

Pandaria
Townlong Steppes (83 - 90) is your best bet...

Most powerlevelers will probably use the bonus objective method for Warlords so I'll skip it.

Be aware. If u want to powerlevel your new shiny twink Draenei with holy horns u must know that this racial ability doesnt stacks with family twink itemes with EXP bonuses. It only gives 8.56% instead of 20% when head(10%),pants(10%),cape(5%),chest(10%),shoulders(10%) are equpped. Without these items it really works as shoud and gives 20% boost. Its really big disappointment for me. The second only usefull skill is actually useless. So much time spent on reputation gaining..sad

Exactly the info I was looking for! Moreso to vary my leveling route between my new Lightforged and my Voidy, so there's not too much overlap. Thank you!