For kicks last night I ran my solo hunter through a couple of AV - 75 Dwarf ...Got between 7%-9% per battle; the last one sucked ...took around 40 min to complete.

I've ran Northrend already with a couple other toons...my girls will quest to 71, and then mix AV with instance runs, trying to keep pace with the gear. As I burn out grinding AV ect ..will mix in some quests to keep it all interesting. Based on what others have said, along with last night as a good example the 71-80 ride should go pretty fast.