If I was to make that decision: XL2420G.
This is why:
1. I am personally against buying things that have been opened and/or used. That means I don't buy refurbs or second hand. However this may not be applicable to you. I am just not willing to accept the risk of buying a faulty product that may or may not be covered by Warranty.
2. You only have 1 970. Unless you plan to either upgrade to Titan X or go 970 SLI, you may not get acceptable frame rates on 1440p without turning down details. (going from a single 970 to a single 980 will have minimal benefit, not the difference between playable and unplayable). If you plan to upgrade often, or if you can also upgrade your GPU along with the new monitor, Swift is a good monitor. If you don't upgrade GPU often, and don't want to upgrade now, stick with 1080p. Besides, DSR exists so you can still get some high resolution goodness if you have the spare GPU power.
3. The smaller the screen, the smaller the drawback of TN will be, assuming you are at the same sitting distance between the monitors.
My 2cents.