While many opinions are fixed from less than stellar experiences from days gone by, today's OC utilities do a very commendable job of OCing your PC. Will it deliver the maximum OC possible for your MoBo / CPU / Memory combo ? No, but these days it will get very close. To get that max OC, your are looking at couple of weeks of changing BIOS settings and the testing to insure stability. I generally take a minimalist's approach ... I'll get what I can by BIOS Editing in a weekend and I'm done.
Here's some test results for Kaby Lake ... reults tanged from a low of 4.7 to a high of 5.4
https://docs.google.com/spreadsheets/d/1NoxceLMU9dnVev8QmYmBT16fnjwrGkwdIRjTQzzKaVk/edit#gid=0
Average OC 5.03 / Average Vcore 1.36
Median OC 5.00/ Median Vcore 1.3
One approach is to use the utilities and see what's the best they come up with. Record the settings when done. With that as a baseline ... try reducing voltages until you can keep that OC stable. Then try inching up a increasing voltages as necessary. Your CLC will be somewhat a limiting factor here. You'd have better temps w/ a moderately priced air cooler like the Scythe Fuma ($45) or Scyther Mugen Max ($37)
As for voltages, it's more than just the VCore setting, it's what boost the MoBo BIOS does with those settings when for example AVX and other modern instruction sets are present. For this reason, I recommend against using any type of synthetic test for OC purposes. What I mean is that synthetics put loads on your system that they pretty much never see again. so what's the point ? Did ya build your PC to get ya name on web site leader boards or to run programs / games ? A soccer mom who's toughest vehicle demand is getting the kids to practice on warm Florida days, doesn't need to test that vehicle going off road and hill climbing. I have had 24 hour P95 stable OCs fail within 45 minutes under RoG Real Bench., The programs on RB will put a tougher demand on your system than it will ever see again in 99.99% of instances. And while the multitasking nature of RB puts a tougher challenge than most synthetics, the temps will be lower. So you don't wind up limiting your OC for temp reasons preparing it for temps it will never see again. I prefer to stay between 1.35 and 1.40, but I don't shy away if I see 1.42 or so during stress testing. With AVX present, the boost associated therewith may even take it to 1.5 for a microsecond and again that's not something I concern myself with.
There's a great Kaby Lake Overclocking Guide on overclock.net created by user's who list their experiences. More than likely you could find someone with similar hardware as your own to target a starting point, you