I agree with gardner. I limit myself on elk and muledeer to about 50. whitetail is about 30, there just too jumpy.
Too answer your question. Do I think a 40 yard shot is unethical? No, not if you can do it. I do, however, think its unethical in the way your going about it. wanting to do a 40 yard shot to see if you can. Bowhunting is about getting close. I have far more respect for someone who arrows something at 10 than at 150.