I used this for my 970. Currently at 191x21 at 1.288vcore 1.26v QPI. You should try your luck getting 200x20 stable. You shouldn't need over 1.3v for 4Ghz. I even have a bad chip and got it stable under that but it did take time. 191x21 is fine at listed volts. 200x20 required 1.337v and 1.28v QPI for me. That guide is fantastic other than you will find lots of ambiguity around the PLL, mine is at 1.55v, its one of those settings that's highly dependent on your chip, going down helps some people going up helps other people. Another important note, bios voltage, sensor voltage, and actual voltage are all very different and I recommend you never actually use the max voltage listed in the guide for long, maybe test if it's what you needed and then back down unless you have a meter to check it. I also saw best results when CPU temps were under 65c.