Out of the box, my 5930K and ram were only running 3.5ghz and 2133mhz mem. I currently have it at an all core 4ghz with the ram at 3000mhz.
For daily use, I can notice the difference, mostly because I am now looking for it.
Being ASUS actually got their overclocking software fairly stable on Intel platforms, especially X99, I can freely adjust speeds without a reboot, and can compare them side to side.
Id say what I have so far is over 5-10% difference, which is quite a bit for nearly zero effort.
People have gotten nearly all the 5xxx and 6xxx chips beyond 4.5ghz, and some all the way to and beyond 5ghz. No fires recorded.
you wont damage anything by having instability because of too low voltage, or bad settings. OVER VOLTAGE will hurt. Just dont go beyond 1.3 volts, and have a nice cooler.
NOW, bad memory voerclocking will lead to corrupted data. SO if you are worried, grab a spare HDD or SSD, boot windows, and go ham on overclocking. Do stress testing, verify everything works, then simply toss your main boot drive back in and enjoy some extra performance.
Overclocking is not a "is it worth it" type of thing. You either enjoy tweaking for a little extra performance, or you enjoy getting more for your money. Numbers games are for people who have the coin to buy the top chips, exotic cooling, and dont mind blwoing a motherboard in the process at times. (or at least prepared just in case)