A GTX 1070 should be OK with 1440p, but may be happier with 1080p.
A monitor that can handle 1440p, “60-75Hz” may well allow for 1080p, 144Hz, too; be aware that most quoted refresh rate ‘claims’ will be for lesser resolutions than any maximum resolution the monitor can handle… a “1440p monitor that can do 144hz” may not be able to do both w/o spending a huge amount on it.
One thing to look for is that you get a 27" monitor with an IPS panel as that’s what your current Dell uses, so that factor of the equation will be consistent.
Edit:
Hop on to PC Part Picker (I can’t do links) & throw your ‘wants’ at it in the Monitor section to give you an idea of your options & likely spend.
I would recommend going for 144hz, but your GPU will not be able to handle 144FPS in most games at 1440P.
It may be in WoW, but your CPU is too slow for 144 FPS in WoW and even on high-end systems you will not be able to get 100+ FPS in a real raid situation.
I upgraded recently to a Ryzen 3900x with 3600Mhz CL15 RAM and a 2070 Super on a LG 27" 1440P 144hz IPS panel.
It’s awesome but like i said, in raids i can barely get over 60 FPS and sometimes even below. Worldbosses drops to 45ish.
Questing is fine and i can get 120-144 FPS most of the time on settings 9.
So maybe the best thing is to get a 27" 1440P with freesync and 100hz or so.