Hi,
1) A good GSYNC monitor is about $750USD.
http://pcpartpicker.com/product/XvfmP6/asus-monitor-pg279q
GSYNC simply means the GPU tells the monitor when to update, so when a new frame is rendered a very short time later it is drawn on the screen. This makes gaming a lot SMOOTHER.
With GSYNC you don't need to use VSYNC (which caps to the monitor refresh rate). VSYNC adds lag by buffering a frame because it's waiting for the next monitor refresh cycle. If you turn OFF VSYNC then you don't get this added lag but you also get screen tearing which can look HORRIBLE at times, or in some cases it's barely noticeable (the type of game, and FPS are the biggest factors there).
2) 1080p and GSYNC?
I'm not sure why you are specifying 1080p. Is it a budget issue?
Higher resolution is better. Even if your game was too demanding you could always lower the resolution. That's not likely to be much of an issue with a GTX1070 though.
3) 60Hz and 144Hz:
If not using GSYNC/Freesync then you have to think about when to use:
a) VSYNC ON
b) VSYNC OFF
c) Adaptive VSYNC
d) "HALF" Adaptive VSYNC
The Adaptive options can be forced on a per-game basis in the NVidia Control Panel. I've used them in several games. It simply turns VSYNC ON or OFF.
*One of the worst things you can do is have a 144Hz monitor and turn on VSYNC. People do it all the time. You get variable frame times which results in STUTTERING. Several factors affect how sever this is but it can be quite bad.
Setup example for 60Hz panel:
1. run FRAPS (or use Steam FPS tool)
2. run GAME
3. Crank visuals to max, observe FPS
4. Adjust visuals and see if 60FPS constant is possible without lowering visuals too far. NO?
5. Adjust visuals so you get 60FPS at least 90% of the time
6. leave game
7. Force on Adaptive VSYNC (NCP-> manage 3D settings-> add game-> ... save)
8. verify it works in game (should lock at FPS cap, but get screen tear if dropping below)
*Substitute 144FPS (144Hz) or 72FPS (144Hz using the "Half" method) as applicable.
4) FAST SYNC:
This is an upcoming driver update that is really useful for 60Hz monitors. If you can output at least 120FPS then it will still lock to 60FPS (same as VSYNC to avoid screen tearing) but will reduce lag/sluggishness by letting the GPU produce frames as fast as it can but then only sample the last one completed prior to when the monitor does its next refresh.
So it's better than normal VSYNC@60Hz but not quite as good as VSYNC@120Hz.
I tested this using NVInspector for COD4 MW. I saw my FPS counter toggle between 120FPS and 180FPS. Fast Sync handles this automatically.
5) Monitor?
I'll give some links, but it really boils down to BUDGET. In general:
a) GSYNC is great
b) 144Hz is better than 60Hz
c) IPS is better than TN
d) 6ms is highest response time I can recommend (the refresh rate also reduces blur/ghosting so 4ms@60Hz has more blur than 4ms@144Hz)
e) 27" is a great size, however 1920x1080 resolution can make the pixels obvious unless sitting far away (over THREE FEET away)
You can use PCPARTPICKER as a guide. I'm sure a few monitors have been suggested whilst I type this tome.
Other:
A lot of hate about GSync's price. Well, that's business. They also came out with something that greatly benefited the gaming community whilst AMD basically attempted to copy them.
Freesync on some monitors is about the same. One some of the monitors it's HORRIBLE. They fixed a major issue affecting performance BELOW the minimum of the range but it still requires the max/min ratio to be at least 2.5X. So, 30Hz to 75Hz is okay, but 30Hz to 60Hz is not.
Some of the Freesync monitors are 40Hz to 60Hz which is so pathetic I'd suggest never using this (not that you can with an NVidia card). You only get the smooth gaming when your GPU is between 40FPS and 60FPS. I won't go any further into it, just as a warning.
**I'll post some monitors below, but maybe COPY this post for reference of the Adaptive VSYNC or other info.