The ASPxTreeListEditor and TreeListEditor can easily work with large amounts of data in Server Mode, and don't require Server Mode to be enabled.
Configure the Windows Forms and ASP.NET FeatureCenter applications to use the same database.
Start the Windows Forms FeatureCenter application and execute the 'Create Demo Objects' Action. This will create 20000 demo objects in the database.
After that, you can observe the performance while working with these objects in both the Windows Forms and ASP.NET FeatureCenter applications.