I have the same problem on a GTX1080. For example Map, Old City Overlook: I have between 25 and 50 FPS after the game ran for some time. Then i restarted the game and suddelny I have 120 fps. There seems some serios problem that needs fixing.
Zoddo posted a question in Pillars of Eternity: Technical Support (Spoiler Warning!)Hey! I think I encountered a gamebreaking Bug that prevents me from progressing further in the game. After graciously avoiding 20 other gamebreaking bugs (I don't know how I did it pure luck I suppose) this one finally got me. So when I entered level 13 in Od Nua there are those spirits you need to get the password from to open the door, so I am clearing the area and after killing the last pack (Pack in the adra shell room) suddenly all spirits aggro me. Ok the problem here now is 1st I cannot get the password 2nd the Spirits are invicible and untargetable but they wreck my party. So then i thought maybe I load my auto save and reload the area by going up and down. Unfortunately the game won't let me because surprise, the raedrics castle bug reappeared and after the load to level 12 the game crashes. So bad luck for me have to start anew after 40 hours, to be honest this game feels more like a beta than a release. In general I like the game it but the combat-gameplay (I only say pathfinding) and the gamebreaking bugs make it more a hurdle race than an enjoyable expierience. Just to add another thing that happened just minutes before, the Spider Guy who gives the quest to collect the stuff in lvl 13 (Adra items) he talks to me and gives me the quest but immediately goes aggro and starts attacking me so I had to kill him and of course the quest failed. This is just one of many "annoyance" bugs I encountered until there so please fix all the stuff so I won't get stuck on the next playthrough which I have to start after the "Day 1 Patch" finally comes out. Here is the Link to the requested files: https://www.dropbox.com/s/uzigyw1tkptftjd/PoE_Saves.7z?dl=0