Hi and welcome to Tom's forum.
Since the GPU will be MSI, I guess that your are going to use MSI Afterbuer. In that order, I suggest you find the max stable OC using all the tools that the software have.
What about voltage? You do not be worried about that, even with the "max" voltage available in the application you won't see a "1, 2 or 3" years life shorting in the GPU, even, I am pretty sure that you can resell that GPU few months or years later without any problem.