More than likely none. The 2700x will perform worse or equal than a 6700k in most of the non multi-thread friendly and non cpu intensive games (mostly all games). The main reason for him to upgrade to a 2700x would be if he's doing something else with his PC (if it's a workstation used primarily for work and also for gaming). If he streams he'll get on average better performance with the 2700x too. He could get better performance on some newer games that are either multi-thread friendly or cpu intensive. Not worth it imo better wait for the new Ryzen cpus or buy something from Intel if he's just gaming they are still king.