gtx 980 ti lifespan

Solution
At the going rate two to three years if intending to the latest games that are released.
But It all depends on how quick the refresh rate of new more advanced Gpu solutions are released by Nvidia and Ati.
That sort of governs what game manufactures can produce in respect to graphics.
DX 12 will be the next reason for most people upgrading to a card that implements the hardware features on the Gpu to support DX 12 instructions.

What it boils down to is what Graphic game settings of a game you are prepared to live with.
As your graphics card ages to be able to play a new title/ game on the market.
It often means you have to turn off a few of the graphics features or FX to make it playable,
with new games.

The choice when to upgrade...
At the going rate two to three years if intending to the latest games that are released.
But It all depends on how quick the refresh rate of new more advanced Gpu solutions are released by Nvidia and Ati.
That sort of governs what game manufactures can produce in respect to graphics.
DX 12 will be the next reason for most people upgrading to a card that implements the hardware features on the Gpu to support DX 12 instructions.

What it boils down to is what Graphic game settings of a game you are prepared to live with.
As your graphics card ages to be able to play a new title/ game on the market.
It often means you have to turn off a few of the graphics features or FX to make it playable,
with new games.

The choice when to upgrade and how long you leave it is how content you are.
And if you can live with turning a few graphical effects off in a game to keep it running at a nice frame rate.


 
Solution
It depends a lot on the games you are playing and the resolution you use.
I went from a gtx580 to a gtx980 and saw no change in same games and a huge change in others. This is because some games are CPU limited, some are not and I run at 1440p

If you are running at 1080p (or less) and you have a current generation CPU then you should be ok for several years to come.