How much of your CPU power can be utilised by Cubase depends hugely on the nature of your project.
If you have many individual tracks with a couple of plugins each, you will be able to run a very high track count, and load up all of your CPU cores to a high degree. However, if you have just one or two tracks with many CPU intensive plugins, routed through some group channels with lots of plugins, you can easily bring your CPU to it’s knees whilst many cores are lying idle.
See attached screenshot showing 24 cores all highly loaded running a Cubase session.
