Great thread! Somethings I've wondered about. Who wants to see one core popping away and the others standing around like a summer road crew? Would improvements in core usage mostly be in program writing or OS? Or both? Could a core program, like SONAR, be written to improve plugin use?

I find one of the biggest hogs is plugins which have their own multi effects chains built in. While it's tempting to keep things "boxed up" and tidy by using these on-board effects, if the plugin is not multicore optimized then you're just hogging a core with them. For instance, take Native Instruments Abbey Road Drums and all their related drum libraries. They have extensive onboard effects, all of which are available as individual VST's if you own Komplete (I think Ultimate). If I load a preset which utilizes the onboard effects, I get core spiking (especially in large projects). However if I turn off the onboard effects and load the same effects as separate VST's, the load appears to be a lot more balanced. So if core spiking is a problem it might be worth looking to see if you have any VST's which are doing too much and whether you can split that work into separate plugins.

Sharke,
Thanks for adding to this thread.  I can see I need to experiment with a few things that I've always taken for granted.

There is a classic saying in software engineer -- "9 pregnant women can't make a baby in a month".  The original formulation was intended to combat the notion that you could get a software project completed faster by throwing more programmers at it but the same logic could be applied to throwing multiple processor cores at something.  Some work just isn't divisible and often when it is divisible, there is so much complication and overhead to coordinating the work that it just isn't worth it.  
 

What worked for me is in Preferences > Audio > Configuration File
Set EnableSetThreadIdealProcessor to False
and
Set MixThreadCount to 1 number less than the cores you have
(for example, if you have an i7 with 8 cores, set it to 7)

Some programm gives you the option to choosecthe thread strategy , i remeber one of the first one that impressed my was. Pyramix ....

For me there s no ideal settings , but scenarios , so i choosecthe option that serve all good ...

As far as code optimisation for plugins management enhacement in sonar , i would says yes , it is possible , i remeber when we passed from sonar 8.5 to x1 having discussions with roland guyz that explained me that the pro channel fx where " kinda closer" in priority and handling to the core of the audio engine ....or some like if i recall well ....

Sonar , imho is by far one of the daws that handles the best already plugins , pdc , and is already greatly optimised , i tested against a lot of other daws inculding studio , differences in cpu hit are not crazy , but there is some ...

Thanks Bob, I will give it a look.