How to convert between flours?
If you are simply looking to convert gluten contents then you can certainly always go higher by adding the correct proportion of vital wheat gluten to dough to get the percentage of gluten that you want.

However there are many other differences between flour bags in terms of processing.  How is the flour ground?  What wheat variety is it from?  Is it white or whole?  There are a lot of variables.

I do speak as someone who has found that Gold Medal is perfectly acceptable for all my baking needs and also routinely uses store brand flour.  Personally I suggest simply trying whatever flour you want to try (not including substituting  bread for cake or something along those lines, that definitely will cause issues) and seeing how the recipe goes.  Determine if a higher-end flour brand is for you yourself.