I gotta agree that the X-bullet, or another premium bullet is the way to go. The lung shot, taking both lungs, is way better than a heart shot in terms of getting a quick kill; anything you want to kill quick shoot through the shoulder, not behind it on a broadside shot. That generates more fragments of bone that do amazing things to lungs and heart, and generally takes the top off the heart as well as both lungs. As far as not ruining meat, the behind the shoulder shot works well, but placement is much more critical. It's easy to go too far back and get liver or , worse, paunch.
I've never seen a center of the shoulder shot not work on any type of game when using good bullets and adequate calibers.
Art, I gotta ask, what bullet were you using in that '06 for the muley neck shot? I've gotten over 3 feet of penetration with my '06 180gr X-bullet loads.