Pre-fetching. You're not actually "using" 8 GB of RAM. Your OS has simply pre-loaded apps, files, etc....that you use most frequently.
Turn pre-fetching off and watch your RAM use drop by half. In fact, if you are using an SSD, you should turn off pre-fetching anyway.
I am using SSD.
Although, i'm browsing 20 tabs on mozilla & 15 tabs on chrome, both installed addons... And i'm leaving opened 3 windowed games(Overwatch, doom & Witcher 3 Gog ver.) plus office word & excel.
Hey, i'm a heavy multi-tasker. ^^
Don't worry about my CPU, it's Core i7-6800K and my network card is helping my - Can i leave? ._.