With this patch there have been various performance optimisations, including:
Added a "Hair Quality" option to the settings under "Graphics". Setting this to "Low" will have better performance.
Improve the performance of both Player and Ghost models.
Replaced surrounding trees with more optimised models. A fog has also been added to the distance with some of the background trees removed for performance reasons.
Improved performance when inspecting notes & items.
Fixed an issue with basement stairs area that was causing significant lag.
Various updates to the optimal graphics settings calculator that determines the best settings for your hardware.