Please try to update You games to the newest versions.
The newest patches should contain some performance fixes.
The patches are meant for "non-Steam" versions of the game.
They can be downloaded from:
Direct links to normal version and GOTY patches
(the GOTY one contains also DLC updates):
Normal version
http://www.1cfiles.com/MoWAS_patch/m...05.13-full.zip
GOTY patch
http://www.1cfiles.com/MoWAS_patch/m...en-2.05.13.zip