Your graphics card will be obsolete before it stops working.
Today, it is not competitive with skylake integrated graphics.
When it no longer can do the job, replace it and keep it around in case you need a graphics card for diagnostic purposes.
As to overclocking, graphics vendors are wise to the practice. They bin their chips and use the best ones in factory overclocked cards.
I would not count on any significant boost from user overclocking.
Moreover, a excessive overclock can reduce the lifespan of your card.
Better to buy a stronger card in the first place.