I just got a brand new computer with much more power in processor. Yes!
But: It seems that CPU threads are not used evenly and few hungry plugins (f.ex. 2 x IzoTope Ozone) can get Sonar crackling and popping. CPU meter tells that the first core goes on 90% when all the seven others work on 5%.
-I have Sonar Platinum with latest version
-I have checked "Use multiprocessor engine" in preferences. Also, "MixThreadCount" in configuration is set to "0", which means using all threads in processor.
-Problem is not only with Ozone-plugins, but all plugins and soft synths.
-No matter if the buffer size is 128 or 512 or 1024.
 
Any ideas how to solve this problem?
Thanks for any help!

CPU meter looks like this.

That's normal. It's just the nature of audio processing that much of the job can't be split into multiple tasks and assigned to different cores. However, you're still getting the benefit of a more powerful CPU because all the other tasks Windows has to do behind the scenes can make use of the other cores.

We have a new feature coming up called Plugin Load Balancing which is designed specifically to handle situations like this by doing parallel processing of effects bins. This will be a Platinum exclusive.

Very cool, Noel. That's just the sort of thing that has traditionally distinguished SONAR from the crowd: not just the glitzy features that make for good ad copy, but real, practical features that make the experience more satisfying.

Thanks. I'm obviously biased so you can take my opinion for what its worth but I think the approach we've taken is quite groundbreaking compared to what others DAW's do in this area.
Most other attempts use lookahead processing to try and solve this, which introduces other problems like latency or induces delay when changing parameters in realtime. Our approach doesn't introduce any latency or side effects like that.

That sounds great!

Would also be nice if we could tell SONAR to run a specific VST instance on a particular core.

Don't know if that is possible or desirable?

Not desirable or easily possible since you want to optimize balancing across all available cores. Otherwise you will just get spiking on a different core.

I think there is a option about this situation, threadscheduling or something.
Make the value 2.
That helps the cpu load unifomrly used so that relax this uneven distribution.

Noel Borthwick [Cakewalk]
We have a new feature coming up called Plugin Load Balancing which is designed specifically to handle situations like this by doing parallel processing of effects bins. This will be a Platinum exclusive.

Good news indeed!  It is encouraging that Sonar software development is headed in that direction. 
 
Most of the hardware architecture of the modern Intel Core platforms has reduced or eliminated the past hardware bottlenecks.  Given enough CPU frequency, memory bandwidth, high speed buses, and so on, the question has become "how many cores/threads do I really need?"
 
I helped a friend spec and build a new PC last year primarily for Photoshop, and potentially, video editing.  I searched for then current benchmarks on multiple core performance.  They were typically i3, vs. i5, vs. i7, etc. 
 
The biggest takeaway I discovered was that 4 cores (or more) were really only of use if the software was written to take advantage of multi cores.
 
The biggest performance gain seen was going from just a single core to dual core, which was huge, then the curve trailed off with the addition of cores/threads.  At this stage of the race it's all about the fastest horse, i.e. the Ghz.
 
I may need that Core i7 after all