Oh good to hear!
G Sync -wise I am using a monitor that has G Sync hardware in it. When customers ask me for a great monitor I always re-sell this model rather, than a monitor that has Freesync and is marked compatible.
ASUS ROG Swift PG279Q Black 27" 165Hz 2560 x 1440 2K 4ms NVDIA G-SYNC, 350cd/m2, 1000:1, DP, HDMI, IPS Built-in Speakers, Tilt, Swivel, Pivot, Height Adjustable, VESA Mount.
It would run your RDR2 in 2560 x 1440 and look unbelievably good. You should get the single player full version again. It's that good. The online version is OK too tho'! =)