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...I have given the windfury enchant a HUGE bonus by simply ignoring the fact that it takes time for the additional swings...
Ah-ha! The extra windfury (WF) hits DON'T take additional time to swing; they're instant. So for every 5 swings with rockbiter, you're essentially getting 7 swings with windfury over the same time frame. The AP bonus on the free swings is just icing on the cake.
Quote:
...So ignoring your own stats and gear...
That's another problem: the extra windfury swings DO take gear into account while rockbiter is a flat bonus unaffected by gear. By undervaluing the base DPS--10 DPS is absurdly low--you're shortchanging windfury. This also means that there is a breaking point in your gear upgrades where windfury will always continue to get better than rockbiter.
Let's assume 1000 AP and one 70.0 DPS weapon (decent level 70 starting stats). Single weapon, no talents, and no crits for easier math--although the extra WF swings can crit, making it even better.
Rockbiter: 70 DPS weapon + 71.4 DPS from AP + 62.0 DPS from rockbiter = 203.4 DPS from white swings
Windfury: 70 DPS weapon + 71.4 DPS from AP + 0.2{2*[70+71.4+(445/14)]} DPS from WF = 210.7 from white swings
0.2{2*[70+71.4+(445/14)]} from WF breakdown: 0.2 from 20% chance, 2 for 2 attacks, 70 from base weapon, 71.4 from AP bonus, 445/14 from WF AP bonus.