If I use any of NI's drum instruments (Abbey Road, Studio Drummer etc) the first core spikes dramatically if I use any of the mixer presets. This is OK in a light project, but once the project starts getting heavier then it seriously affects things and the first core spikes into the red (all other cores showing relatively low activity). 

The thing that confuses me is that I have Kontakt set up to use all 6 cores in the options. Yet when using as a vst in Sonar, it doesn't appear to spread the load of those mixing effects at all. 

In fact first core spiking seems to be an ongoing problem for me with Sonar in general. I have changed the relevant parameter in the config file as others have suggested. Yet still, that first core....oh man!

I've experienced the same.

Mixed blessing that Cakewalk lets you see the cores.
(iZotope's RX2 Advanced also takes advantage of the multi-cores, but doesn't show individual core usage....)

Something I learned was that there is no core balancing like you'd expect. Supposedly it's in the OS, and that's the one single reason I'm considering Windows 8... I don't need the touch interface, but I would seriously like to see more evenly distributed core loads.

Try this link:
http://www.gearslutz.com/...awbench-results-2.html