RE: 40 yard shot
I agree with others that said "if you are comfortable with the shot---take it". However, skill and practice must back up the shots that you choose to take. In addition, each situation will be different due to the alertness of the animal, weather and even to how confident you feel at the time of the shot.
I know people who will take a shot at 60 yards with the mentality that "you won't get them without shooting at them". That is what I find repulsive. There are some people that have no business even taking a 25 yard shot.
With my statement in the 1st paragraph, I do agree that there should be some distance that most responsible people will refuse to shoot, even though they believe that they have the skill to make the shot. I passed a shot at a P&Y buck at 50 yards this year feeding out in a picked corn field. I knew the exact distance (range finder) and I have the skill to make the shot. Weather was favorable and deer was not the least nervous. I just did not think it was a ethical shot.