Bill pretty much covered all the bases.  Based on some of the posts earlier in the thread, I would add that it sounds like possibly CPU speed is being throttled and the OP needs to:
 
- Disable Speedstep, C-States and Turboboost in BIOS.
- Set Windows power management mode to High Performance.
 
Here are some more salient points from Cakewalk CTO, Noel Borthwick on CPU usage when bouncing/exporting:
 
     http://forum.cakewalk.com/FindPost/3286635
 
Bottom line: "old code that would be cumbersome to update" is horsepuckey.

timg11
I'm still not seeing proper use of multi-core, or even one core, for compute-limited tasks. (@jimkleban, I am not using the built in graphics in the Intel chipset- I have a separate NVIDIA video card)
 
Example Scenario:  File / Import Audio.  Import a 1 hour long MP3 file (44 khz stereo).
On a 4 GHz i7-6700, this takes about 20 seconds.
Resource Monitor shows processor utilization of about 3%.  Detailed CPU view shows one core at about 50%, others unused.
 
Example Scenario: Normalize Track.  Takes about 10 seconds
Resource Monitor shows processor utilization of about 2.5%.  Detailed CPU view shows one core at about 50%, others unused.
 
What am I missing? Why is the CPU underutilized? I know multi-processing is not perfect, and I won't see 8 cores at 100%, but I expect better than 5% total CPU utilization while I'm sitting waiting for a single-threaded (UI blocking) task.
 
 

Have you tried this? https://bitsum.com/parkcontrol/
 
I've been using it and have had a solid and marked performance increase. It's all about spreading the load out over your cores. Maybe it's working in addition to recent CW adding "load balancing." Not sure, as I'm not a big techie. All I know is it's been working great for me. Your mileage may vary... there's a free version and pro version for about 10 dollars.

Thanks for the helpful responses.
 
I thought about disk limiting, but Resource Monitor doesn't show any high utilization of disk (based on its "queue length" metric). The task is pretty simple: import one 44.1Khz stereo MP3 file of about 1 hours length into one Sonar track. No plug-ins. I can copy the source MP3 file (650 Mbytes) to another folder in 2-3 seconds, but Sonar takes 20 seconds to import.
 
While the BIOS, windows power management, and core parking are interesting, I don't think there is any CPU limiting going on at the system level. As a counter-example, I can encode HD video from MPEG to H.264 with Handbrake, and see all CPU 8 cores go to 100%.  After a few minutes the CPU fan on my otherwise silent system starts to become audible. That occurs without any special settings on my part (unless Handbrake is doing something fancy "behind the scenes" - but that would beg the question why doesn't Sonar do the same?)
 
I guess it could be considered a "feature" that Sonar limits CPU use to keep the CPU fan quiet, but I'd rather have the option to get the full speed when I'm just sitting and waiting for task to complete.

timg11
The task is pretty simple: import one 44.1Khz stereo MP3 file of about 1 hours length into one Sonar track. No plug-ins. I can copy the source MP3 file (650 Mbytes) to another folder in 2-3 seconds, but Sonar takes 20 

Copying a file from one directory to another on the same drive is just re-write of the file system tables; little or no data are moved. Importing an MP3 to SONAR requires reading the compressed file from disk, decoding it, writing an uncompressed .WAV file to disk, calculating transient marker locations, and writing picture files to the picture cache. The two operations are not remotely comparable.