Hello @BloodyIron, we're using one issue report per unofficially supported game title, so I've gone ahead and transferred this issue report to https://github.com/ValveSoftware/Proton/issues/2628#issuecomment-573318091.
Oops sorry about that. Looked it up and didn't initially see which one I should post in. Thanks for your help though! :)
Compatibility Report
System Information
FPS for the game is utter crap considering how beefy my computer is and how old the engine is. It's a DirectX9 game and I get 30-45 FPS, when I should be pulling well over 300-450FPS. It also forges my graphical detail settings (apart from resolution) each time I launch the game. Game also encounters stuttering as if it is a frame time issue frequently. Completely terrible performance. Bioshock Infinite (written on the exact same engine) gives me way more FPS on much higher detail settings.