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From what I have been told, the ranking gain is less than the loss in link juice you would have by doing 301's from http to https, therefore there is no actual ranking benefit. If there was , I personally think everyone would be doing it. Like Chris says above, John Mueller said in a recent hangout,that if you had 2 identical sites in everyway and both was josling for position, then the https would take preference but personally I am waiting for ranking benefit to atleast equal the loss from 301s before I consider doing it. thanks Pete