That is a wise choice, I did not use FastSync as I have a gsync monitor. Is there any difference between the two?
Cheers matey. Oh yeah, big difference, they're totally different functions and grats to you for getting a G-Sync monitor, I'd love to have one. <best green with envy face>
G-Sync: without it, the GPU and monitor work at a fixed refresh rate eg 60Hz, 100Hz etc. For smooth, stutter-free motion, the GPU should be rendering fast enough that vsync can be used to maintain a solid framerate, matching that of the refresh ie one rendered frame per refresh. If it drops, then you get all that glorious stuttering we pay so much money to get rid of with a high end rig. G-Sync (and adaptive sync generally) works the other way, where the monitor is synced to the framerate of the GPU, so there's no fixed refresh rate from the monitor. Thus fluid motion is still achieved when the GPU can't render a high framerate and it helps with latency too.
FastSync: this relies on out and out brawn from the GPU (and the CPU too, but to a lesser extent) and works with a fixed refresh rate monitor. Here, the GPU isn't synced to the monitor refresh in the usual way. Instead, it's allowed to freewheel, rendering frames at a speed above the refresh rate eg 120-200fps for a 100Hz refresh monitor. However, all those extra frames are not sent to the monitor, only the one immediately before the next monitor refresh cycle. This maintains the benefit of smooth, tear-free motion as if vsync was on, with the lower latency of vsync off and is especially noticeable on a fast first person shooter game. The cost is that the graphics card works harder, running hotter and using more memory, so that 8GB framebuffer suddenly doesn't look so huge any more. If the GPU cannot render frames faster than the monitor refresh, then the effect is lost. This is why a high performance PC is needed for this feature to work properly. Of course, the monitor refresh could be dropped to 60Hz say to maintain those extra frames, but the effect is much better at 144Hz monitor refresh and higher.
Presumably, this can be used with G-Sync to maintain smooth motion when the framerate drops below the monitor refresh, eliminating stutter under almost all conditions, with the cost being latency at those lower framerates. Note that a G-Sync monitor will work like a regular monitor above and below the G-Sync framerate range, hence it should work ok with FastSync. I see that you have the same Palit GTX 1080 that I did (isn't it quiet!) so give it a go and let us know how you get on.
Current AMD cards don't have this killer feature, so I hope it will be available with Vega, otherwise I'm not interested.