Boosting with a 60 on RAF accts ???

I understand that most boosting is done with 70-80 lvl characters, but my question is "which class would you use to boost a RAF team up with if the booster was only lvl 60"?

I ask because I finally plan to start a RAF team of 5 boxing. After the initial 1-60 run on all 5, I'll be looking to use the main account to boost another 4 toons. I don't forsee having a high enough playtime during the RAF period to get my main toon to lvl 80. 70 may be a possibillity. So hence, I might be boosting with a 60-ish toon.

Which class would be best? or should I invest the time to get to 70?

I'm targeting 5-box teams of Pally, Mage, Shaman, Druid, Priest.

If you have one, 60 pally is fine. Otherwise, roll up a DK when you can. They basically start in t4 gear anywho and takes no skill at all to get from 55 - 60