What's beautiful, when does ugly stop? As far as I am concerned, overbore is when you reach the point of diminishing returns. If 60 grains of a certain powder gives you 3,000fps and 89 grains, in a larger case gives you 3,050fps, then you have slightly more speed, and substantially less barrel life. Everybody may have their own personal yardstick of what is reasonable and practical, and it changes, depending on the application.
Good hunting. LB