Visual Studio 2010 supported 64 bit Test Agent which used to allow us to do 64bit test runs as explained here. But Test Controller was capable of running in 32 bit mode only. As a 32 bit process, it was limited to 2GB of memory. This causes scale issues sometimes as QTController process starts throwing “Out of Memory” exceptions as it approaches 2GB limit. This eventually causes abort of Load Test run.
Good news is that Visual Studio 11 Beta supports 64 bit Test Controller. You need not to do nothing special to run your Test Controller in 64 bit mode. It will automatically run in 32 bit / 64 bit depending upon architecture of Test Controller box as Test Controller process has been targeted to “Any CPU” platform . So this means that even though you are doing a 32 bit run using 32 bit Test Agent boxes then also your Test Controller might be running in 64 bit mode if Test Controller box is 64 bit box and vice-versa.
Just to re-iterate, Below shown option in Test Settings has nothing to do with Test Controller mode. It decides about Test Agent mode as explained here. Test Controller mode (32 bit / 64 bit) will be decided by architecture of Test Controller machine.