Nostalrius Begins - Quality wow vanilla realm (1.12)

I was wondering, when does leveling become the hardest imo? 40-50, 50-60? Just asking. (i guess it would be the 50-60 part, because of the xp required, but some might argue that the quests between 40 to 50 are not that abundant

30+ when you have to start leveling up in highly contested areas and have to party up to do ANYTHING(kills your exp) or else you'll get gang rped.

Otherwise it would be 47+ ish for me, after Tanaris.