Just a couple notes to add to the consideration.
Who cares about viewing angles when using a monitor? You sit directly in front of the screen regardless. This isn't a TV where multiple people are sitting from all sorts of angles.
Color accuracy is also not so important with gaming. You can run programs to help calibrate to be close, but unless you are doing graphic art, can you tell if something is a miniscule off? You aren't comparing it to anything and you'll never know.
Looking crisp is a real advantage to an IPS screen. You will notice a difference in gaming.
120hz is a real advantage with a TN screen (if you get a 120hz TN), as it makes things smoother, and for me, eliminates motion sickness that I get with FPS/hz below 80.
A 1080p resolution also takes less GPU power to run, but to get 120 fps/hz gaming would require about the same GPU power or more than the IPS screen.
120hz gaming usually includes 3D gaming, which many are surprised to learn is really awesome (surprised because of all the people who parrot that it's a gimmick with no 3D gaming experience).
There are reasons to go either way, but if you are comparing 1080p 60hz TN to a 1440p 60hz IPS screen, there is little reason not to get the IPS screen, just make sure it's got low latency. Latency causes me to get simulator sickness, for me that is nausea, others get headaches or eye strain.