The Alienware X51 is a nice desktop with plenty of power and small footprint however I will stick with the M17X laptop. Just to note (they are not light lol). We have a Dell Precision laptop purchased to run SolidWorks and that is also quite heavy, However I prefer the Alienware as it has true dual NVidia graphics cards with auto update for drivers etc

The XPS Dell is definitely not mobile but the X51 is a mobile desktop in is size to a point.

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