Hi Preben,
I'd use your own data to calculate this, the data that you can usually find from vendors and blog posts like this are usually far off. They're outdated and aren't taking into account the specific industry (with its extensions) that you operate in. So you're basically making an assumption on what could be your performance where you'd be off with xx% at least.
Take your own data from Google Search Console and calculate it that way, with that it's a specific as possible and you can segment on the data that you're looking for.
Martijn.
