when you have 6/6 items the last bonus is 5% crit damage while under the effect of fury. it does not give you the 5% crit damage while the buff is on.
on a side note, the red moa pet buff (fury) does not buff you sometimes even when your right next to the pet…and also when you use the pet skill while the pet is attacking the mob it takes forever to use the skill, and i have to spam f2 like 5 times or more to make it use the skill once.