Estimated number of users by model

Hello everyone , 

I want to know the number of users each model can support based on your experience.

I know that sizing must be based on other metrics: use cases, activated licenses, ISP throughput, interface configuration, etc...

But , The number of users can give an idea of ​​the size of the environment, so I want to know how to relate the number of users to the range of fortigate models that might be suitable. I then use these metrics to determine the best model among the other models in this iteration.
I'm talking about the F and G series.

Thanks for your support

Regards