If you can group ALL of your arrows within a 3" circle at 60 yards id say shoot em at 60 if they are still. I like to think in a deer hunting situation that roughly twice my average group size should be thought of when shooting at a deer at the same yardage... You've gotta take into consideration all of those other things....
I will say that if you can shoot 3" groups at 60 all day long, you should go to Vegas next year and shoot the indoor Vegas world championship. Those 3/4" X's should be nothing if you doing that good at 60
Usually about 40k goes out to the winner... And most of those pros dont even shoot that well at 60.