If you haven't heard, the Visual Studio Load Test team is in the process of releasing some custom tools for load testing SharePoint. While the basic web test works nicely, you'll now get some more flexibility to interact with SharePoint components like lists, document libraries and the query service. You can find the latest bits in the Visual Studio 2012 Update 1 CTP 3 release. The SharePoint specific stuff is in the file titled vsupdate_KB2707250.exe. While there isn't much documentation yet, stay tuned to the Visual Studio Team blog for more information. I've used and seen the tools in use. They're a great step forward for load testing SharePoint. These tools will only be available for SharePoint 2012.