Got around to trying the new demo and the graphics settings is an interesting approach. I think there's an issue with the niagra system that you're using for the death effects. The game was running fine until the first fight when the frames dropped a lot once I killed the first enemy.
By the way, when you change graphics settings, it seems like all of the death effects that have already been triggered do so an additional time. At least, it did when I changed the graphics from medium to low. That crashed the game by using up every last bit of VRAM memory. You might want to throw a "do once" node into the death sequence to see if that stops that from happening. That is a good indicator that the niagra is too demanding though.