Sour Dough bugs are really interesting to me. I think people make too much of an issue with the sourdough starter. I do not remember how old my starter is but it is old. My sour milk culture is better than 20 years old.
My sourdough starter is very slack meaning more water than flour which I keep in a quart canning jar. The reason for slack is to keep the mixture from crawling out of the jar and all it want is to feed the yeast and bacteria to keep them healthy.
When I want to make sourdough bread or other sourdough products, I start with some sourdough starter and mix 50:50 with flour and water and pitch (beer term) a small amount of sourdough starter into the mix and let it ferment.
My sourdough will be different than Chef Jacob in Western US or Mucho in Canada. I cannot brew a wild beer like in Belgium or make wine like in France because my local conditions are different.
I live in Kansas-US and use Kansas flour, the yeast and bacteria are local for my location.
I can buy San Francisco sourdough mix like anyone, but I do not believe the mix would last very long before my local conditions would over run the San Francisco sourdough mix and become a different mix all together.
My policy is to go with what you have and to go with flour that you can buy locally from the store. If you like Gold Metal flour then continue to use Gold Metal flour.
The strong will survive in the mix!
Chris