I've actually never tried boosting in RFD. I may try it soon though as I have a group of mages at 22 just starting out in SM.

I think the reason most don't boost past 60 is like you said, no RAF bonus and mass killing with 1 character gets slower and slower as you level. You just can't kill enough of them faster than they kill you. Boosting depends on total damage per second. When you can gather tons of mobs at a time even protection specs can do massive dps. DPS = XP per sec.

I am going to try 60+ boosting by specing my 4x druids resto and seeing how much they can keep me alive while I try to gather huge groups of Outlands instance elites. I'll let you know how it goes.