Originally Posted by
Eroginous
G-Sync is a great feature that helps provide a quality gaming experience while working to eliminate screen tearing (Vsync disabled) and input lag (Vsync enabled). Without getting into a huge long post about the benefits/drawbacks of Vsync, just know that Gsync is one of a few different techs developed to fix Vsync. The downside? Unless you buy a monitor that is G-Sync enabled, you cannot utilize the feature, since it's proprietary to the monitor. Additionally, G-Sync is Nvidia only, so the tech is not compatible with Team Red (AMD). From what people have said, G-Sync is a great feature and works as advertised - if you embrace the proprietary nature of it and understand they may suddenly stop support for G-Sync before monitors have widely adopted the standard.
For a time, AMD was working on their own form of adaptive sync tech called 'Free Sync,' meant to be a semi-open source tech (works with any monitor) widely available as long as you had graphics card support, but was not ready for market by the time Nvidia went all-in with G-Sync. Now, Nvidia has another tech called Fast Sync, which is debuting on 10 series cards. Instead of dynamically adapting to enable/disable Vsync to remedy screen tearing or input lag, Fast Sync works by scanning individual frames as they are buffered, intelligently selecting and displaying only the ones that are tear-free, at a rate as fast as the monitor will display. This is one of the reasons I suggested a 144hz panel instead of a 4k, since you'll be able to leverage Adaptive Sync technologies more than you can leverage higher resolution ATM.
If you do decide to spend the extra money for G-Sync, it will work in tandem with Fast Sync to give you a buttery smooth gaming experience, even if you're not always getting 144 FPS or more. Keep in mind that without G-Sync, you'll still experience performance issues in games when you're below the refresh rate of the monitor, but it's unclear how that affects 144hz panels at this time. I don't have one to test so I can't really suggest which way to go on that.
As for the rest of your PC, it looks great (a lot more current than my build and I do fine with lower specced hardware @ 1080p), I don't think you need to do anything more than upgrade monitor/GPU. If you were setting aside a larger budget, that means you can do stuff like consider a multi monitor setup or picking a higher end option like the 1080 if the 1070 was your original plan.