I noticed that when I set the CPU meter in SPLAT to system performance, zooming in and out even when sitting idle cause one of the cores on my system to spike. It's not the first core, it's random across the other cores. This is not a perceived problem, I'm not having an issues. My card is a about a 6 year old NVidia pci express model, just wondering if upgrading to a newer card would bring down the CPU spike? Or is this just normal on the pci/pcie bus. 
 

I have very old computer (CoreDuo) and the latest NVidia (not most powerful, but for sure sufficient for Sonar). And I have big spikes when zooming. So I do not think that is graphic card related and is normal. I never had problems with that, I guess Sonar is correctly written and give required priority to audio related real time tasks.
In general, CPU load indicates that there is something to do. That is not a direct indication that you do not have resources for particular task. F.e. if you start some "burn in" test like Prime numbers calculation, at least one core will be 100% loaded. But that does not automatically influence what you do in Sonar, even without explicit manually set priority.

have you tried disabling load balance ?
I had spikes on one core and when disabling load balance on projects that didn't effectively need it, it helped out a lot.