It looks like you have several issues, Im also skipping all the potential software issues because you said you reinstalled everything.
For the high single core usage, it depends what you are doing, you should be able to see what program uses these resouces, if its windows, look into windows optimization sripts, if the source of high usage is not showing up on device manager, its drivers, look into installing older versions.
For the stutters, if it is a pc freeze, try to lower mouse dpi but have higher sencitivity instead, read up on switching gpu interrupt mode too. If the stutter affects only part of your system, its probably a mbo fault, try to use different usb ports and upgrade/downgrade bios.
For low fps, i'd check gpu settings especially g-sync
Sorry for such a generic response, more info is required to narrow it down. Your specific mbo is known for memory issues so try also running with a single stick of ram
