Dark Messiah is known for FPS problems in certain places no matter how fast your PC is. The horseback ride into the town as soon as you start game, Gettign onto the galleon due to loads of water and Source engine water can kill performance if ther is lots of it.
FEAR I read some time ago that logitech G5 mouse drivers can cause conflicts in FEAR.
http://forums.logitech.com/t5/Mice-Hard ... td-p/23474
As for Mirrors the only thing i can think of is because it uses unreal engien 3 it gimps some ATI hardware, my 1950pro wouldnt run UT3 any higher than 30FPS on lowest res and settings but my older X850 could easily get 70FPS on lowest settings