think carefully about what reps you want to grind, most probably don't have anything useful for your priest esp with wotlk so close (i don't think its worth grinding to exalted for anything now). it would be faster as well to invite a healer and 2 dps and just run the heroic version, imo. assuming your priest has some shadow gear of course, its much easier DPSing 2nd account than trying to tank and heal.