Why not keep Bonner? There is no point in giving up a rotation big man if you don't have to.
Mason Jr., Finley and Mahinimi would be a much better trade. Why would you keep Finley? There would be no minutes for him, Bonner on the other hand would still have some minutes available.
Actually I wonder if the Warriors would be interested in a someone like Haislip instead of Mahinimi? He might fit into their run and gun system better. How sweet would that be? Then you can trade Bonner and Mahinimi for another big if you can match salaries

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I wouldn't include Bonner unless you get another big man back. For example you can add Bonner to those three try and get Turiaff back as well.