I have same problems after patch 1.55. I noticed longer texture and object loadings, also smaller frame per second rate. I also noticed that changing one graphic option kinda refreshes the frame rate to playable point for a minute or two, but texture and object loadings are horrible all the time.
I have Radeon HD4850, 4 GB of RAM and Core 2 Duo 2.6
It was very fine on normal with some high settings. After patch 1.55 its annoying and sometimes unplayable.
BI please help us :( !!!!