Fan of Knives is 80.

I helped my roommate boost some toons.
Tried 50-55 via quests, combat rogue at 80th with mostly iLV226 gear could one shot pretty much anything.
The only mob which took longer was the 61 elite dinosaur in Un'goro; the 60 elite guys were a couple hits.

But 55-60 in Ramparts with a pally in iLV200 to iLV226 (Ulduar/Naxx BoE's) no Conquest badge gear yet, leveled them a lot faster.