It doesn't matter if the 85 is RAF linked or not.
I'd definitely link them, as you get free characters from the granted levels, the mount and get a month free.

What does matter is that each of the toons who are playing meets the requirements for RAF.
So if your chain is:
A > B > C
A > D > E
Where "A" is the boosting account, and BCDE are the accounts being boosted.

For RAF to work, since A is over 79th (RAF stops at 80th), we know that the A/B and the A/D RAF links will not work.
But as long as the B/C and the D/E do, then they get the bonus experience.



You basically take your team through quests until 10th, which opens up instances.
Almost all the mobs you kill are going to be grey for the booster, up until the very end.

If you were to group BCDE and go into a very high instance for your level.
Let's say Deadmines at 13th level.
Aside from the trash at zone in, once you hit the elite mobs you'd likely be done.
Sure, killing one might be 1,000 experience for each toon.
And with an 85 in the party, they only get 250 per toon.
Note - I'm picking numbers out of the air here, for illustration.
A pull of three mobs would likely wipe the entire party, given they are elite and much higher than the party.
With an booster aggroing a group of mobs, all the threat on the higher toon and none on the group who are sitting near zone in... there is no threat for the lower toons.
There is also no threat for the higher toon, who can kill 40 mobs at once...
And 40 x 250 = 10,000... which is a lot faster experience than the lowbies can get on their own, even if they aren't getting as much per kill.

You can get instance levels (minimum level to enter), from google: wow +wiki +instance +levels.

When I did it (pre Cata), it was something like this:
01-10 Quest
11-16 Deadmines
16-20 Stockades
20-45 Scarlet Monastery
45-55 Strat, Scholo or BRD.
55-60 Ramparts

If RAF has gone to 80th...
60-62 Blood Furnace
62-65 Underbog
Not really sure what is appropriate beyond that.



You can always quest for a few levels.

And you can take your group into PvP.
The brackets are x0-x4 and x5-x9.
So 14th/19th (and to a lesser degree 13th/18th), and 24th/29th (23rd/28th), etc... are prime levels to PvP.
Whenever your side would earn honor, as a BG objective completion or victory, that is experience.