I just started playing on Wednesday, and I remember the performance being great the first day I played, but lately it's gotten a lot worse. I went from FPS in the 85-100 range to hardly ever getting above 50. I wasn't sure what the reason was at first, and tried lowering my graphics settings to compensate, but more recently I was digging around and noticed through task manager that the game was only setting it's affinity to 2 cores. If I force it through task manager to use all 8, then my FPS returns to that 85-100 range I had before, but every time I re-launch the game, it changes back to just 2 cores. I'm not sure why the launcher would be doing this or if there is a way to fix it so that it uses my hardware properly. My system information is as follows:
i7-3770k processor
16GB memory
GTX 1080 graphics card
ASrock z77 Extreme 4 motherboard
Windows 10 Professional