Never max out the power/voltage slider right away and just try to overclock, do it in small increments. It takes longer, but it'll be safer for you to do it that way than to just right off the bat bump it up.
Yes it is safe, I had to crank the voltage up to 100% and power limit to 112% to get a 200mhz gpu oc and a 400mhz (800mhz effective) ram oc. I also use msi afterburner and it won't damage your 1070 as both of mine run this oc full time. The 1070 is safe up to 125% apparently but msi can only set up to 112%.
Mine is stock 1500mhz core so yours might oc better or worse depending.