New Rig: Can disabling Hyperthreading sometimes enhance SONAR performance?

Here is an example of X3d playing 5 Kontakts and a loopback channel doing the recording.
An external tool (Fractal Tune Smithy) is generating the 5 channels of MIDI through Loopbe30.
Notice the CPU performance control in Sonar is very smooth and so is the Performance Monitor.
Open the image in a new tab to see it full-sized (1920x1080).
 

I think you should keep hyperthreading enabled in the BIOS, but what you probably want to do are two things:
 
1) Disable core parking
2) Improve multi-core load balancing (A SONAR tweak)
 
Disabling core parking will mean none of your threads will sleep, but they all will be available to handle loads, and the SONAR tweak will more evenly allocate, to available cores, your SONAR project loads. Thread scheduling makes a considerable/significant difference/improvement, but one thread will always take a little bit more of the load than the others.
 
Below are guides for how to do those two things. The guides are excerpts taken from this thread. Since you are running Windows 7, you might find the complete tweak guide an interesting read: http://forum.cakewalk.com/The-Sonar-x64Windows-7-x64-Install-Tweaks-Compatibility-Thread-m1862515.aspx
 
"- Core Parking:  Is a new features in Windows 7 that may be very handy for laptop computers, but not very convenient for systems where high performance is needed at all times.  You can google it if you want to learn more about it.  But, to disable it, you'll need to do the following (skip this if you're not comfortable editing the Registry): 
  
Go to Regedit and find the following key (use the "Find..." command under "Edit" to make this easier): 
  
0cc5b647-c1df-4637-891a-dec35c318583 
  
Within this key, change the values called "Value Min" and "ValueMax" to 0.  You'll have to find the key a few times (press F3) and adjust the values each time.  The number of instances depends on the number of power profiles in your system.  When you're done, do a cold shutdown/power on. 
   
[Thanks to TomG and sky60234 for providing this awesome tweak]
"
 
"9- Sonar Tweaks: 
* Improved Multi-Core load balancing  [From Noel's SONAR 8.3 Log] 
  
Since all systems are not made equal we decided to make this new scheduling mode configurable. 
From the help file, the new aud.ini option to control this is: 
  
ThreadSchedulingModel=<0 - 2>  
Type Integer  
Default 1 
  
This variable goes in the [Wave] section and controls the interaction of the main audio thread and worker threads on multiprocessor systems when the Use Multiprocessing Engine option is enabled. Depending on the system, a particular model may result in less glitching and better overall performance. The values are as follows: 
  
............0 = Same as previous versions of SONAR. 
............1 = (default) Better thread balance. Model is more efficient and can provide cycles for other tasks. 
............2 = Additional worker thread is created. This may result in improvement with Quad processor systems or higher. Not recommended for Dual processor systems."
 
To change in SONAR X series, open Unified Preferences view, and under Audio>Configuration File (Advanced view), look on the right and find the section "ThreadSchedulingModel". Change the number to 1 or 2. Check which one works best for you.
 
Hope that helps.

Normally, threads are managed by the application, e.g. SONAR (which does a stellar job of it, btw). Every program starts out with a single main thread, but can spawn additional threads whenever it makes sense to do so. Hyperthreading is Intel's way of automatically getting multi-threaded performance from single-threaded programs. 
 
How well it's going to work depends on the type of program you're running, although Intel has been tweaking it over the years to make it smarter. The i7 has a whole new hyperthreading scheme that's reportedly a big improvement over the old Xeon. I would expect it to have the least benefit for applications that are designed to make use of multiple cores, although it apparently does help even SQL Server, which is the king of multi-threaded, multi-core apps. That suggests that the new hyperthreading scheme is a big improvement and might even provide some benefit to a DAW. Even if the DAW itself doesn't benefit, it might make background processes run better, freeing some CPU cycles for the DAW.
 
I'd answer the question experimentally. Play back the same project with and without hyperthreading enabled, and compare CPU usage in both SONAR's indicator plus the Windows Task Manager. Then go with whatever works best.