With RAF Xp I would not suggest doing Only pvp. You dont get much xp for pvp and you want to level as many toons as possible during RAF XP. That being said, 5 mages, disc priests, druids and ele shamans are alot of fun in pvp. I am currently doing 5 resto druids no RAF just heirlooms and its ALOT of fun. Disc Priests can kill my entire team with pennance but I avoid them. That said Disc Priests Pennance is SUPER OP in lower BG's. You can kill anyone and they will almost never break your shield. I moonfire x 5, Wrath x 5 and only got the priest to 50% when he rebubbled. Mages as arcane do huge burst and lets face it you cant lock out 5 mages so something is gonna die. Ele shams can heal and do good dps (chain lightning is super strong in bg's).

Its all personaly preference really with 5 toons coordinated assault stuff dies really fast and you just sit back and get raged at.