This video is a recording showing how long it actually took to load a few hundred thousand users into Exchange 2013, the loading seems to be severely rate limited, either by the .NET bloat, or maybe Microsoft was just playing safe to avoid having to debug any race conditions. This is one thing that I like about open source software and that is that the programmers do not seem to have any fear of running things at full speed and then will fix any bugs that show up subsequently. I remember how slow Windows Server 2008 used to be and some of the pauses that it would do didn't seem to make any sense. If you tried to install Exchange 2010 onto Server 2008, then you would sometimes get these extremely long pauses where hardly any CPU was being used and there would be little hard drive activity, so it was not obvious why the install or updates were taking so long.