Sorry, I also should have clarified - I'm now aware that you had a readme file with suggested settings etc, and I ignored it. I actually enjoyed the framerate as it was for me throughout the game before that point because it went along with the drunk disorientation vibe I was getting. I was playing on default settings because I felt they were fine at the time.
My PC isn't really for games, btw. It's quite old and clunky, so I wasn't expecting things to go very smoothly.