I made bunch of benchmarks of the framework 4.0 and older and I can't understand why the same code is slower when using WPF compared to Windows Forms:

This is the code, it has nothing to do with the UI elements:

        Random rnd = new Random(845038);
        Int64 number = 0;
        for (int i = 0; i < 500000000; i++)
        {
            number += rnd.Next();
        }

The code takes 5968ms - 6024ms to execute in Windows Forms and 6953ms in WPF.

Here is the post with the downloadable solution: http://blog.bettiolo.it/2010/04/benchmark-of-net-framework-40.html