dontlistentome :
I think what your friends are trying to tell you is you are thinking of spending more on one component, the videocard, than your entire computer is worth. That's a big imbalance.
*IF* that's what they're saying, it's still wrong. Hell, a friend of mine put together a new system a couple of years ago, and of the $1500 it cost, half of it was the GTX 1080 (which had just come out at the time). He already had the 2560x1440 monitor (144Hz refresh I think)
It also neglects the fact that the video card is portable over to a newer system.
Whether this interpretation is true, or not, I can't really see why/how OP's friends made their determination that it's not going to work.