1200p is only 11% more pixels. For a videocard of 1070/980Ti class level, the performance difference between 1080p and 1200p should be negligible. I am also not aware of high end 1920x1200 monitors that are a match for 27-32" 2560x1440 60-144Hz ones.
There are some excellent 120Hz 1080p VA panels for examples for which a 1070/1080 level card makes sense for competitive PC gamers.
http://www.bit-tech.net/hardware/monitors/2014/07/21/gaming-monitor-roundup-2014/11
Anyone who plays CS:GO or BF4 or Overwatch would benefit from a faster motion and less blur on a 120-144Hz panel over a 60Hz one. But that only nails the coffin for 22-25" 1080p 60Hz panels even more.
It is possible to bring nearly every GPU to its knees on a 1080p/1200p panel by enabling 4xSSAA in modern games.
Answer this, if you had the $$ to buy a 32-40" 4K 120Hz OLED or a 3440x1440 120Hz G-Sync/FreeSync monitor, would you still be gaming on a 1080p/1200p 60Hz panel? V
People become comfortable using the same headphones/speakers and monitor they have because they view it as a sunk cost. It works for them and they keep using it without questioning it. The biggest system upgrades I've ever been happy with were the SSD and my monitors, not CPUs, videocards, RAM, mobo features, etc.
If I could afford a 40-43" 120Hz OLED HDR for PC gaming, I would buy one tomorrow. Notice how almost no one on this forum who had a Titan X/980Ti/Fury X/295X2, etc. was using them for 1080/1200p 22-25" gaming? There is a reason why that is. It's because it doesn't make sense to pair high end graphics cards (that require high end resolutions to fully take advantage of them) with a $100-200 monitor.
Some people love the feeling that their game runs at 70-100 FPS on a 1080p 60Hz monitor since they feel good about "reserve performance in case they need it". My view is that by the time it's needed the person who bought a $229 480 8GB will just sell it and buy a much faster $350 videocard anyway.
If you read my posts, I don't agree with buying a $400-700 card and keeping it for 5+ years. Over that period, the extra performance of the 1070 over 480 won't mean squat. Would you say a $399 GTX670 "outlasted" the $249 HD7850? Both are slow now and it's only been 4 years since those cards launched. In fact, even in 2015, 670/7850 were already too slow. That's why future-proofing with a 1070 for 4-5 years doesn't make any sense for someone who doesn't mind buying/reselling once every 2-2.5 years.