Some opinions on leveling

I have a strange configuration. Basically I have 2 toons I am trying to catch up to my 3 70's to make a full team. I have a warlock (64) that is doing well and a shaman (40) that I have been ignoring.

I am going to drag my shammy through the old stuff (BRD, STRAT, BRS, DM, etc) forever more. Would it be better, xp rate wise, to just use 2 70's plus my shammy? My trouble is that I would either have 70 pally tank and pew pew 70 fire mage, with no heals buy my shammy, or tank and 70 holy priest is no pew pew. I am taking a vacation for a couple weeks and won't get to experiment until I return but I wanted to see what others have found. I know using 3 70s and my 64 gimps her xp a bit :/

Thanks for the opinions.

Curious to know why you say no heals from your shammy, a 40+ shammy has some decent heals by then and can only get better :P I would go the pally/mage/shammy route personally, won't take long to get some more levels... or... pally powerlevelling the shammy on it's own?

My shammy is currently full enhancement. I could respec him restro, I'd just need to replace his gear.

Don't you need 3 to get the group bonus?

Yes you need 3 for a group bonus, but if you got a decent pally to powerlevel with I don't think an extra few exp is gonna make a huge difference. If you want to get group bonus add the mage :)