the little sow hog i stalked and killed that's shown in my avatar was hit in the lungs and nicked the heart at about 13 yards, she traveled about 15 yards and was dead in literally a few minutes. it'd be boastful for me to say that a 13 yard shot is a 'gimme' for me, as lots can happen on the hunt and i was blessed with what i'd consider a clean, fast kill. praise God.
all i can say is i'll assess every shot opportunity at whatever distance the quarry is, and make an ethical decision - and if the green light is on, i don't really think distance, i think 'spot' and concentrate on just that.
also depends if the hunt is ground or air based. different distance/aiming thinking for me if i'm up a tree. same is true for those wired texas whitetails!
when my game is on, 30 to 35 yards can be fine. in the best of all worlds, 15 to 20 yards inspires much more confidence of a good hit.
oh yeah, those short little 5 yard shots can be every bit as tricky as a 35 yard one! ask me how i know! :D