Mostly people are achieving greater speeds by boosting. Since you are leveling 5 of the classes you chose you are probably doing so by questing which is why it is slower. At this point I would suggest to you, if you have a main that can boost, is to boost the 4 toons then grant levels to the first toon.

If you don't have a main that can boost and you have extra gold you can pay an 80 to boost your 4 toons, and again grant levels to your first toon. I am just assuming you did your RAF A-B-C-D-E.