XG248Q (Asus 240hz) Overclock

[Zaxeq]

So I have a GTX 1080 and I wanted to see if I could overclock this card, the displayport cable that came with it was a 1.2 so I bought a certified 1.4 displayport cable and the highest I can get the overclock is 249HZ, anything over pixel clock of 549 does not work, either says no signal or out of range. Is there something I'm doing wrong because apparently 1080s and 1.4 cables are supposed to be able to handle up to 1300 pixel clock? So why can't I go any higher?

[Q83Ia7ta]

It's hardly possible if even possible even because it's limited by monitor firmware. How they will sell you brand new 360hz monitor if you can overclock 240hz one?