There is very little waste in a busy slice location.
The point above that you can do both is a good point.
Slices and personal pies are not an either-or proposition. They are also very different businesses. The personal pie is quick as lunches go, but it is not ready to go. I think that if you are in a good slice location, you will find that personal pies are slower, less profitable and will cost you sales because in a good slice location, people do not want to wait.