I have completed the quest for finding proof of Grubb, so I don't know if I'll ever have need to go back into Sunken City. While there, though, I noticed after crossing the second gate there was a huge slow down to the point where I couldn't walk and turn at the same time (key combination of up/right or up/left would only have my avatar walk forward with no turn). I had to walk a step or two, then turn right or left as needed, then another step or two, and so on. Very frustrating, and I'm glad I finally got through it.
