Hi from France
I have this very strange experience, I open a model Project with my three favorite VSTi with Cubase 8.5 in Win 8.1 and the charge of the processor is around 30-40 % high, without any action. If I launch my arturia Spark EDM for playing, it is saturated and crakling sound… 
On the same machine, booting with another hard disk with Win 7 I launch the same project, the processor’s charge is showing 3 % and I can record without trouble at all.
The project is the same, the machine is the same, only the system is different…
Of course, I have closed all unusefull process on both system.
I have WIn 8.1 installed on a PC based with a new SSD Nvme Samsung 950 Pro, supposed to be three times faster than a conventionnal SSD with 32 Go of Ram and I7 6700K, the Win7 HD is an hybrid one…