I have tried running graphic settings at low, and shaders turned off, and game play is great for about 15minutes, then it lags to unplayable and I log out, and back in (which for some reason during this episode takes couple minutes extra); however, when I log back in, game play is again great for another 15 minutes or so.
I have actually tested this on 2 different systems (1 desktop (custom and question on specs) and 1 laptop Dell XPS16) and have the exact same behavior. I was questioning my internet and thought I would look at the forums, and found this post. Looked appropriate to add, and I will follow.
Desktop:
Windows 7 32 bit
Pentium Dual Core E5700
Nvidia GeForce 8400 GS (I do not see this on the list in the post (Desktop Performance Guide), which is a great reference btw, so could expect issues with this vid card I think.)
Laptop:
Windows 7 64bit
Intel Duo CPU P8600
ATI Radeon HD 4670
These specs are all listed on the referenced link, and think that there may be an issue to investigate here.
Any suggestions welcomed