I've created a very simple project to highlight the problem :
a mainwindow with two buttons that opens a second window, one with a stackpanel and a label, second with also a docksite.
I tracked the time for New() procedure :
Window without docksite : about 4ms in debug, 2ms in release
Window with docksite : about 1400 ms for both configuration.
I'm quite surprised by the time needed to create a simple UI with empty dock site !! What is the trick to improve the time needed to load UI using Actipro component ?
PS : I can provide the VS2010 project if you ask for