Headbands of Mental Superiority exist. Therefore, they are possible. Therefore, they are possible to you.
If you know how, that is. Does a former third-circle wizard of Golarion know how? Can she figure it out?
The Pharaoh of Osirion has only a +4/+4/+4, wrought by one of the few archmages in history that could be bought at any price to spend that much time; and an archmage is also strong. Greater items than that are generally made by gods.