Thanks for the links, I may check them out, if I get the time... Even though you did shamelessly advertise it on my welcome thread :P
As far as the pH level of the human stomach acids go, it varies, as it's name denotes, it's acidic in nature. Otherwise, it wouldn't be called Human Stomach Acid, generally however, it'll be around the range of 1.4 to 3.6 given a lot of different factors about the person in question. It's about as strong in acid levels as a car battery, but because of how our bodies work, generally we would never know just how acidic it is, unless someone has stomach lining issues, or is graced with the unfortunate situation of Acid Reflux.
And yes, I knew about Down's Syndrome being that way.
Cheers~