Re: Xbar–R or Xbar-s
Personally, I use sigma on all my x-individuals charts. But, most of the literature (especially from Dr. Wheeler) advocates the use of range.
I can say that Dr. Shewhart in Economic Control of Quality of Manufactured Product does compare the use of the range to the standard deviation, and makes an argument that the standard deviation is the more statistically powerful of the two. The difficulty was that in the 1930's, range was much easier to calculate than the standard deviation.