The quickest way of doing 50-60 will naturally be to do the new dungeons, so without having finished the 2.55 questline so you can access all that, levelling would be pretty slow. I doubt we'll see a repeat of what the Northern Thanalan FATE situation was in 2.0 - I got my DRG from 41 to 50 in about nine hours of fating thanks to that, which is hardly the way you're meant to experience the game.