ASRock Z170 Pro4s Overclocking issue

Hello. So, i've upgraded my pc to the next configuration: cpu i7 6700k + cooler Scythe Ninja 4, Asrock z170 pro4s motherboard, gpu card gtx 1070 and 16gb ddr4. I started to OC my cpu to see if i can make it stable at 4.5ghz, because that's the point where i want to keep it. I stabilized it at 4.5ghz(45x100mhz), all core option in bios, at 1.32V and LLC Level 3 (on Level 1&2 it wasn't stable, got blue screen for each). On idle when i turn on my pc, on cpu-z the voltage shows up 1.312V(even though on bios it's Core Voltage Manual set: 1.32V), and because of the LLC Level 3, in stress test with prime95 and aida64, after 10 minutes each, it was stable, but the voltage was 1.280V(with LLC Level 1 1.248V and with LLC Level 2 1.264V), temperatures were pretty fine, 75 celsius degrees in stress. Everything was good, but after 1 hour since i ran the tests, when i was in desktop just doing some ordinary things, nothing to use the cpu even at 10%, i got a blue screen and restart. I said, ok, let's get down to 4.4ghz( i didn't wanted to raise the voltage  to see if it will be stable), i set the voltage to 1.30V same LLC Level 3 (again with Level 2 and 1 it didn't worked, blue screen), and again it passed the stress tests, and, after 30 minutes, same thing in normal desktop, blue screen. I set it after to 4.3ghz at 1.28V Level 3 LLC, and for 3 days it was stable, no errors.
I want you to ask if it's possible to stabilize it at 4.5, what other things should i try? I have a friend with a better mobo, an Asus Maximus VIII Impact, and with MY CPU, it was stable at 4.5 @ 1.25V. So, it's because of my mobo? Is it capable only for 4.3ghz? If you have more questions, i am here to respond you all, thanks.