Framedrop when going into battle

[Thomas]

This problem is probably not a problem with the AI. It is either a slowdown due to the physics, but since you have a good computer I doubt that is the cause, or it is because of graphic-card issues happening with the skinning.

You could try downgrading the drivers as suggested here:
http://frictionalgames.com/forum/showthread.php?tid=944

In any case it is strange, since you have pretty much the same specs as me (actually even better).