Well, one good thing about overclocking Hawaii chips (Might as well be the only good thing about overclocking them compared to other cards

) is that they can take quite a lot of punishment. I mean, you wanna throw more voltage at them? They can take it. Temperatures are getting higher? They are designed to run at up to 95 damn degrees Celsius. You can hammer them all day long with benchmarks while overvolted and overclocked, they'll take it. Not that NVidia GPUs don't take overclocking well or something, but I wouldn't push that much voltage through any NVidia GPU (Maybe on the beefier PCB models while water cooled).
With that said, GCN reaches a point of diminishing returns quickly. My MSI 390x does 1210MHz at +100mV, but at the cost of power consumption and heat. Seriously, it peaked at around 340 watts (around 300 average) for the GPU and close to 600 watts for the system. Not to mention that I slowly boiled in that room. I have now set it to 1050MHz and -75mV and it's quieter, cooler and WAY more power efficient. It consumes like 175 watts average (Never went above 200), as if I have a 980 in there. Nice stuff.
Now, I will apply my overclocked profile when playing Witcher 3 or games that are as demanding as that, but for everything else, I'll back down. That's just my 2 cents though.