We recently integrated performance point monitoring server into our sharepoint 2007 enterprise farm.

We have 2 web servers and 1 application index server in the sharepoint farm, with a sql cluster. All servers running server 2008 and sql is 2008 standard.
With the installation of monitoring server we bought another seperate sql server that is running windows 2008, sql 2008, database services, reporting services, integration services and analysis services. This sql is 2008 but with sql enterprise.

So on the web servers we have ssrs and the add-in installed for 2008 and it all works fine. The ssrs on these servers are setup as scale out deployment and running enterprise ssrs.

Is it required that the ssrs running on the sharepoint web servers be enteprise edition to match the server that handles the reporting which also is sql server 2008 enterprise?

We tried it with sql 2008 standard on the web servers but never worked, but it works fine now with matched editions and versions of sql. Just want to make sure as enterprise sql can be costly.

Is there some microsoft articles to backup the matching of editions for this scenario?