Seemed to be OC related - closing MSI Afterburner didn't seem to do anything, but I kicked everything back down to stock and it seems stable now.
Weird that it is only this one game out of all of the other demanding titles I've tried.
Metro games have always been a bit odd. Very demanding and good looking, but I recall my GPUs tend to get very hot and the Last Light benchmark was a bit finicky. The benchmarks themselves are a lot more demanding than actual gameplay, but I over time I found that the LL benchmark will really tell you if your OC was too high.
Might want to play around with a more mild OC once you're done with the game.
Edit: Seems like DLSS only gives around a 6 frame rate jump for me. From around 52 to 58, or 48 to 54 depending on the scene. This is the desert area with the brush outside of the train which is by far the most demanding part of the game.