Hi and welcome to the forums!
I don;t know where everyone gets this melting factor from, as that could never happen, your looking at hundreds of degrees celsius for that to happen, when you do a good overclock, you won't tend to go over 80 degrees with a setup like yours, especially with your CPU cooler.
As you may know the 970 chipset is not very good for overclocking, and you are quite lucky, you have one of the best overclocking 970 boards around!. You can go to 4.2-4.3Ghz without a problem, it's safe and will certainly have respectable temps with your CPU cooler. Don't attempt to ever overclock around 5GHz, especially with your motherboard, you will cause damage, and not due to melting, but heat is a contributing factor but instability is the main issue, to get to 5GHz, you need custom water cooling and a 990FX chipset.
Thanks, what would be a good voltage for 4.3? Last time I tried at 1.4125 and my system sort of froze.