RAF comes down to the relative value of money vs time.
Either approach will work.

If your existing accounts (aside from the main, with the 85's) don't have a lot of toons you care about...
You can always RAF four new ones, from the original.
You could even server transfer one "booster", with all your heirlooms, gold and a bank full of sellables...
And level on a new server, with a lot of other boxers.

It doesn't take that long to level, even without RAF.
Pick a team you don't have, and would like to have that are not Death Knights.
And then level that team to at least 55th, so you can make DK's.
I'd probably go with five DK's at once, since the quests/forced storyline are fun initially but not something I'd want to do again.