So Gsync + HDR is broken for me, or should say gets really bad results.
Running 4K everything maxed with a 2080 Ti @ ~2100-2150mhz (TAA, no Reflection MSAA) and using Vulkan as DX12 causes crashes on the benchmark for me.
-No G-sync / No HDR = ~42 FPS
-No G-sync / HDR = ~ 42 FPS
-G-sync ON in NVCP (V-sync OFF in-game and OFF in NVCP) / No HDR = ~42 FPS
-G-sync ON in NVCP (V-sync ON in-game and OFF in NVCP) / No HDR = ~ 42 FPS
- G-sync ON in NVCP / HDR ON = ~29-30FPS
So that is almost a 50% jump just in FPS from not having both G-Sync and HDR enabled. I think I will play with HDR ON and G-Sync off for now.
My next steps is to try and get SLI working. Following this thread closely to see what ppl can do. It seems that there is a slight change down the road official SLI support might come to RDR2 depending on what you read from this profile. Who knows if that really is the case, but hopefully the community can iron it out at least. The SLI Profile for The Outer Worlds from the community has worked out well so far for me.
https://forums.evga.com/Red-Dead-Redemption-2-SLI-Support-m3005252.aspx