- Opening XAML files fast:
Developing WPF screens in Visual Studio 2010 SP1 using the Windows Presentation Foundation Designer, even in code view, can still be a drag as it’s slow and especially when opening a file.
Always open documents in full XAML view
The first step is to not open the design view. To do so go in “Tools > Options > Text Editor > XAML > Miscellaneous”, and check the “Always open documents in full XAML view” option:
Using the Source Code Editor
Openening XAML files in the Code View is better but if that’s still not enough for you as it was for me, here’s the ultimate tip: instead of opening them using the default editor (Windows Presentation Foundation Designer), open them using the “Source Code (Text) Editor“: it’s as fast as opening a classic XML file, and you’ll still get the auto-completion, which is not the case when using the “XML (Text) Editor” (yeah, I tried that one first 
).
To set that up, right-click on a XAML file and select “Open With…”, then in the dialog set the “Source Code (Text) Editor” as the default editor by clicking on the “Set as Default” button:
Now try opening one of your big WPF screen, and taa-daa!! It’s lightning fast!