I'm still awaiting some Sandra results you guys might want to share.
I'm still awaiting some answers to my questions above. Without knowing what your configuration is, test results by other people are not going to help you.
1. CAS timings
2. Exact make / model of RAM
3. RAM configuration - 3 x 4 GB modules? 1 x 8 GB, 1 x 4GB? Bank ID's?
4. GPU - this does make a difference. New drivers can opt to share some of the CPU RAM, especially for certain games / mm apps.
5. Disk type(s). Programs load from the drives. Levels load in CS:GO from the drive, and much data may be cached / stored dynamically (e.g. as you move around a map). The system's swap file also relies on disk. And check the SMART info on your drives, while you're at it. It could be that one or more of your drives in the system is failing, generating errors that the system has to mitigate.
There is a whole variety of scenarios that could occur as a result of failing bits of seemingly-unrelated hardware. Network adapters, audio, GPU, drives, DVD, PCI bus, etc. are all candidates to generate system interrupts and would become especially noticeable during CPU load.