fakeroot make-kpkg buildpackage

When I run make-kpkg --initrd buildpackage with concurrency_level set to 17, all cores are at 100% according to gnome-system-monitor, when running the cc1-jobs. When I run fakeroot make-kpkg --initrd buildpackage with concurrency_level set to 17 as well, the cores stay at around 40-60%. What am I doing wrong? Do I have to use fakeroot-ng? p.s.: The xsltproc-jobs take 100%, btw. I am confused.