Sorry for the off topic but Rock, Paper, Shotgun did a revisit of the Sync monitors in anticipation for Freesync 2
https://www.rockpapershotgun.com/2017/02/02/freesync-vs-g-sync-revisited-freesync-2-is-coming/
Interesting read!
Having used both, on Asus PG278Q and the MG278Q; I must say I found them to be identical for all my use cases and gaming.
Only advantages G-Sync had for me was SLI support, and Borderless Windowed support, but even AMD have the latter now. Don't think they support FreeSync with XFire yet though.