On the gum arabic/gomme, when I have used in soda making I found in my bench trial, family preference, that they did not like it when I used more than 1 cup gomme syrup/gallon, so I just used no more than that and used other sugar of choice to make up any difference. And the gomme syrup really does make a difference when working with oils/zest, etc.
On the cream of tartar for soda base, I have only used it in the invert syrup capacity. I learned from my Grandmother, her 'formula' was pretty close to the links I referenced.
Motto: quel che sara sara