UPDATE:
After returning the first Dell XPS 15 that I bought, which featured an i5 processor, I bought the same machine but with the improved specification (i7 processor, 16gb RAM, 512gb SSD):
http://www.dell.com/uk/p/xps-15-9550-laptop/pd?oc=cnx5512&model_id=xps-15-9550-laptop
First impressions using ArchiCAD are that it works very well. It seems responsive and sharp. There are still a few minor distortions when using the fly through navigation in the 3d window, but these are no big deal. Files open quickly and there is no lag when using the wall and beam tool in the 2d window as there was with the previous machine.
All-in-all I am very happy and would certainly recommend it to anyone looking for a top-of-the-range multimedia laptop to run ArchiCAD on. It's certainly fine for high-end professional use.
One thing though, Laszlo Nagy is right, it’s probably best to just uninstall the GeForce Experience application as that has been known to cause issues with ARCHICAD (his words). I did and I haven't had any problems like I did before.
Paul Griggs BSc (Hons) MCIAT MCIOB
Chartered Architectural Technologist
AC23, i5 3570K Processor, 16gb RAM, NVidia 570GTX Graphics Card, 250gb SSD Drive