Capacity management and sizing for SharePoint Server 2013
http://technet.microsoft.com/en-us/library/cc261700.aspx
Performance and capacity test results and recommendations (SharePoint Server 2013)
http://technet.microsoft.com/en-us/library/ff608068.aspx
Estimate performance and capacity requirements for enterprise intranet collaboration environments (SharePoint Server 2013)
http://technet.microsoft.com/en-us/library/ff758657.aspx
Software boundaries and limits for SharePoint 2013
http://technet.microsoft.com/en-us/library/cc262787.aspx
Architecture design for SharePoint 2013 IT pros
http://technet.microsoft.com/en-US/sharepoint/fp123594
Capabilities and features in SharePoint 2013
http://technet.microsoft.com/en-us/sharepoint/fp142374
Hardware and software requirements for SharePoint 2013