Windows 8 Cubase Pro 8 perfomance?

I regularly get random performance peaks whilst using Cubase. However today, I was mastering an EP, I was using a couple instances of Ozone 5 and L2, started getting clicks and pops, Cubase vst performance meter was averaging at approximately 80%. When I checked my task manager, I noticed that it apparently was only taking up ~20% CPU power… is this some sort of bug? Is Cubase maybe capping the amount of CPU power I can use?

My specs:

Windows 8
Cubase Pro 8.0.5
Intel i7-4770k @ 3.5Ghz processor
cubase performance.png