http://bugs.winehq.org/show_bug.cgi?id=17956
Summary: BGII: Sluggish performance with fixpack installed Product: Wine Version: 1.1.18 Platform: PC OS/Version: Linux Status: UNCONFIRMED Severity: normal Priority: P2 Component: -unknown AssignedTo: wine-bugs@winehq.org ReportedBy: casperbruun@gmail.com
Installing the BGII Fixpack causes some very annoying slow downs while playing Baldur's Gate II: Shadows of Amn and the expansion Throne of Bhaal.
Small thread about the issue on the official fixpack forum: http://forums.gibberlings3.net/index.php?showtopic=14537&st=0
Installing the core component of the fix pack will make the game overall less responsive (opening menus, clicking on "Cast spell", etc), longer load times when loading a new game and a 1-2 second freeze when selecting the main character.
Running other mods on your BGII installation causes no such issues, it is only this specific part of the Fixpack. As can be read by following the link, no such issues occur while playing the game from Windows. I can verify that as well.
I am honestly at a loss as to what is causing the problem.