If you want to go from 5 accounts to 10, you'll need five additional accounts either way.

It makes more sense to RAF link the 5 accounts together.
If your existing accounts are A-E, you could link the new accounts F-J from one of the existing accounts.
Something like:

E -- F -- G -- H
E -- F -- I -- J

I'd recommend a boosting type toon (probably a tank) although any 80th AoE class would work, to be transferred to the "F" account.
Although you'll group F-G-H-I-J together, if they're linked from E, then E will receive a free month of play and an RAF mount, plus get granted levels from F (which would only be the cascade granted levels from G and I, but that's still free levels).

Basically treat F, G, H, I, and J as five brand new accounts, as far as leveling goes.
Definitely take advantage of RAF, getting to 60th any combination you find fun, or that you missed.
Along with whatever you want to compliment your existing five accounts.