I'm off work now, so I'll explain the voltage / frequency curve. Now, when you set an offset overclock, you're allowing the software to create what roughly equates to a stock voltage / frequency curve by itself....it's essentially just raising every point across the curve up by your offset amount. As you can see below, I set an offset of +150 on the slider, but looking at the curve, it set +143. That's because 150 was outside of the 12mhz steps that Pascal uses. Disregard that for a second, and just look at the voltage. See how the curve that it's set, has a voltage for that clock at 1043mv? That's going to allow the GPU to try to run your prescribed clock at that voltage, before it bumps the voltage up. Micro-changes that like inherently cause instability.
Now we'll look at the voltage / frequency curve method. I've set an offset clock of +110, to get my voltage points close, then raised the frequency points for the voltages above 1043mv to higher clocks until I got to the voltage and frequency I was targeting. In this case, the exact same 2164 core clock (+143), except now, it's not going to try to run 1043mv, it's going to go straight to the 1081mv I've prescribed for it to run, and won't go any lower, unless it starts warming up, in which case, it would drop a step and run 2154 @ 1075mv. This GPU is under water, so the likelihood of that happening are slim and none, but.....on air, it could.
Anyway....the meat and potatoes: Using the offset method and trying to get a decent overclock is pretty foolish. You'll get much better results with the voltage / frequency curve. And THAT, is something I'd expect to see in an "overclocking tutorial" on Pascal.
Enjoy