User blog comment:Kaido King of the Beasts/Chapter 784 Prediction: Gear Fourth/@comment-26494402-20150421123340/@comment-176.145.198.155-20150422192321

It may be a little of the two. Half of Gear second's speed and half of Gear 3rd strenght. If it's that, Luffy can do more damage on Doffy and I can understand why Luffy didn't need it until now (like for Noah). Using the faster Gear 2nd and the more powerful Gear 3rd is the best way to finish ennemies so he didn't need it at all. Doffy is stronger than anyone Luffy fought post-timeskip, to fast to be hit by Gear 3rd and Gear 2nd don't do much damage on him. If Gear 4th is as I said, it would be logic to use it now.