1080 is fine for low settings at 1440, a 1070 would even do in most cases. If you want to play high/ultra you have to get a 1080ti and even then some games wont reach 144hz. I had a 1070 before my 1080ti with an 3440x1440 ultrawide (3k) and it was definitely serviceable. I would get the 1080ti and look forward to the CPU upgrade.
Nvidia probably isnt releasing anything soon, the thing with PC gaming is being stuck in a perpetual state of waiting for the next best thing so if you can buy a 1080ti now just do it. you will be smiling from ear to ear believe me.