The grubs on timeless isle are the fastest way to get xp at 85+.
olny problem with this area is competition and pvp if you are on a pvp realm.
Otherwise, with a group of 4 you can easily do elite or non elite cranes and turtles at 85.
basicly non stop farming starting with grubs, then cranes in the area then turtles by ally fp all the way to horde fp..... Then back to grubs.