I wondered why my Game (Marble Blast like see my other post) was running slowly when adding more triangle meshes.
After some research i found that the Triangle Mesh Bounding Box is always +/- Infinity which isn't very good for the CollisionSystemGrid.
This problem can be fixed easily by moving the line 87
boundingBox = new AABox(rootNodeBox.Min, rootNodeBox.Max);
in Octree.cs to line 98 where the correct rootNodeBox.Min and Max have been calculated.