"Houston, we have had a problem", a crazy modder supplied the chips with 1.6v even if it's rated 1.32v max. He is even speaking of going up to 1.8v...
7.5k resistor should be the way to go for the actual clock cap. it gives 1.35v
You do risk destroying the chips if you overvolt them. I don't know the absolute limits for the 55nm process (google has not been very helpful so far). Even if they work at a given voltage, the devices may degrade and die at some later time.
I've gone up to 2.06v on gridseed. and by the time they will blow, I think they won't be profitable anymore.
Anyway, it's all related to power draw/kh
Pushing too hard gives less profit because it uses way more power.
I can confirm 7.5k resistor draws 80 watt at the wall on each Fury but will allow to overclock up to 381 clock
so around 15% overclock for double the power draw.
if we extrapolate gridseed results, 1.5 to 1.6v should be safe and could give an extra 15% in hashrate, but will probably draw over 100 watt at full load.