Looks like that's common for shadow priests. Had a lvl 60 sp attacking my team(lvl52ish at that time) last week too. Ofc he hadn't even the chance to kill one of my toons.

But back to quests: My highest char hit 60 yesterday, I'm still in the old world and gaining much xps through quests there. And I haven't even touched Silithus yet. The downside are ofc the items in the old world.

The more outlands quests I keep for lvl 70 the better. 25k Gold is a long way -.-