I had the exact same setup myself when I started boosting:

Main1 --> RAF1
Main2 --> RAF2
Main3 --> RAF3
Main4 --> RAF4
Main5 --> RAF5

I grouped Main1 and Main2 and RAF1 and RAF2 and boosted toons. The downside is that you only get half of the RAF gift levels since you're only leveling two, BUT you get double xp. Then you do some server transfers when you're done so you don't have to keep paying for the RAF accounts.

In this way I was able to boost Priests and Druids to 60 in about 4 days real time and then gift Warlocks from 33.99 to 60.99.