That also depends on the size of your screen. I am guessing you game on a Monitor?
On a 55inch TV, 4k is quite noticeable and I have fiddled around with resolution settings in games to tell the difference and I can easily see the improvements on my screen.
Most PC gamers use smaller monitors around the 22inch to 32inch size. That size is perfect for 1080p and 1440p however if you went with a 55inch to 75inch TV, you can easily see the difference between 4k and 1440p. However I am in the minority here because majority of PC gamers don't use a TV to game, they normally opt for refresh rates in monitors instead.
I will be buying a decent monitor next year as I am moving house and I am looking at something good, if I stick to a 32inch size I probably wouldn't need 4k and can lower it to 1440p and increase framerates in my rig instead.
The only reason you'd notice a difference is because of the lack of a 55" 1440p TV. Otherwise, in a like-for-like situation, the difference gets smaller (hence why many PC gamers opt for 1440/144Hz over 4K/60 on 27-32" monitors). There's not a huge difference between those resolutions. HDR makes a bigger difference.