capacity planning for power bi report server (PBRS) import (cached) mode

Hello everybody.

If i understand, the document 

Capacity planning guidance for Power BI Report Server (PBRS)

https://powerbi.microsoft.com/en-us/documentation/reportserver-capacity-planning/

address aspects for Live/DirectQuery connection capacity planning - when the analytical queries itself are being executed on external analytical system (SSAS).

In a case of  Cached data PBRS handles analytical workload internally  - any ideas how to estimate the hardware in this case?