i tryed 5 prot, for fun, long time ago in pvp, in Bg.
basically with crappy gear, rare+crafted epics items.
oom is a real issue and lack of mana make healing capabilities...almost useless.
mana is the main issue. but it requires better testing. the positive thing was HoJ spam
pve? dps is too low, you probably run out of mana too fast.
But ...with gear... and if anyone could constantly switch tanks during fights...maybe some heroics bosses are... possible(??) ... not sure.