IBM WCM multiple libraries and performance

A customer askme last week if the we separate WCM code from content has impact  on WCM/Portal performance.

My answer was No, there is no impact but the customer need an official response.  I opened a PMR and receive the response today :

As noted, the WCM best practices are to separate the content from the design.
For example, see the following link:

Multiple libraries does not incur additional performance penalties since references are by UUID, which is independent of library.