If you're boosting...
And you'd be able to boost very well with an already 80, and somewhat (maybe very) geared toon, at least to the upper 70's...
You could also run the Pally through Cata content to be 84/85 in quest stuff, before RAF, which would make WotLK 80's dungeons quite easy to boost in.
I'd transfer the one toon.
I actually did faction change + server change, on five toons... which sucked for the costs, but the Magtheridon guys are great and I'm having lots of fun there.
A (Pally) > B > C
A (Pally) > D > E
Boost four toons on BCDE.
End up with:
A: 1x Booster +4 Granted (2 from B & 2 from D) +2 Additional Granted (Because B/D each were granted two, letting them grant one more each).
B: 4x Boosted +2 Granted (From C)
C: 4x Boosted
D: 4x Boosted +2 Granted (From E)
E: 4x Boosted
That's:
A = 6 new toons (and the Pally)
B/D = 6 new toons
C/E = 4 new toons
A toon leveled from 1st to 80th, with RAF can grant 39 levels (not 40, for some reason)...
So each pair of toons, can grant 78 levels between them.
So the toons who are receiving granted levels, would be leveled to 2nd... and be as close as possible to 3rd.
So after gaining 78 additional levels, they're 80th and very close to 81st.