How long does a graphics card last, roughly?

I’ve always been very careful to make sure nothing happens to mine. I change its thermal paste once a year, clean the dust from the cooler frequently, I’m always checking the temperature, I don’t let it go over about 80 degrees, and I’ve always taken care of it like this because only I know how hard I worked to be able to buy one.

Now my little card is going into its fifth year and I’d like to know roughly what the maximum lifespan of my little card can be. Should I already start getting ready to buy another one? Are these GeForce 40x series cards worth it? Is the performance difference compared to the 20x really that big?