I do not like the term "lowest caliber choice". It all depends on the shooter and his/her confidence/ability/judgement and situation. My situation might be different than the next guy's. His or her ability and situation might allow the use of a "lighter than normal caliber". You might use better judgement than the average person on a specific situation and can get away with a lower caliber.
The point is, the term "lowest", excludes too many options and creates too many debates without knowing all the facts. As we all know, we have all heard or read stories, maybe even experienced situations where unlikely calibers were used to take down the largest beast. You know what I mean, ie. a .22 short for deer, .222 for Polar Bears, 7x57 for elephant, etc, etc. etc. Yes, almost every single rifle caliber, will kill almost every sort or land mammal on earth under a specific circumstance. If the shooter has the ability, the situation presents itself, using the right bullet, and the range is correct, you could probably kill a Cape Buffalo with a .22 magnum shot through the eye. Now would the average, sane person try this? No. However, the lowest caliber could be used, in theory.
I am not advocating the use of lighter caliber bullets. I am on the total opposite side. I do believe and wish that more hunters would practice with their firearm of choice and know thier limitations. I am stating that too many opnions are given without thinking or knowing all the facts or situations. A prime example; is that the .270 is the lowest caliber you should use for elk. There are probably many on this web site that hunt elk with a 25-06. Now should everyone do it, no? The guys that do it, know thier gun, use the right bullets, and practice. "Lowest caliber" is too broad and generic. Why don't we change it to "Recommended Minimum"???