Giving it vigilance would make it a total stall card; your opponent loses a chumpblocker each turn while not being able to attack you..
I do think that, at three mana, most opponents will not have had a change to play a decent amount of creatures and will not be able to kill it in combat (by blocking with multiple creatures). Therefor, I would like to suggest we leave it at 7/7 for 2WW and see what playtesting brings..
(keeping 6/6, or Vigilance in mind of course)
Deal?