I have recently upgraded from 512mb 8800GT Overclocked to a 1GB GTs 250 and am puzzled by your performance or lack of it

. Im using the same drivers as yourself but have no drop in gameplay. I am unsure of the FPS as until reading this thread I didn't know how to, although control room is very smooth with no lag. I am playing on 1280 x1024, with everything maxed, i'll have a proper look at the settings tommorrow and let you know
Playing on Intel Core Quad Q6600 @2.4Ghz
3GB RAM (unsure what type)
Vista 32bit SP 2
Nvidia 1GB GTS 250 Overclocked
p.s. Try dropping back your drivers to older versions, may help.