I've recently upgraded to an 8-core CPU from a 6-core CPU and have been playing with a bunch of multi-threaded applications while monitoring core utilisation.
To date, Sonar has the most even core loading of any other multi-threaded app I have tried, including another DAW and video editing apps.
From modest projects up to multi-track monsters with huge numbers of FX, Task Manager shows incredibly even core loading. Very nice to see :)
Sonar X2 64-bit
AMD FX-8350