I don't own the Dell XPS model, however I do have an Asus with very similar configuration, with nvidia discrete graphic card with optimus and an integrated Intel card.
I'm running Ubuntu 12.10 on this laptop and in my experience the Intel card is more than enough for office work and I don't have any problems connecting it to a large external monitor via HDMI and working with both monitors simultaneously.
Installing the latest bumble-bee allowed me to turn the discrete card off to extend the battery life, and by using optirun I can even run an occasional OpenGL requiring app.
The video in 1080 HD format plays just fine, and the desktop effects also run without too much problem in my case.
So I believe that you should be just fine with that setup, provided you don't need the nVidia card for a day to day work.
But on the other note, why not buy some similar laptop without the discrete card at all, if you don't intend to run graphic heavy stuff on it, and save some money on the way.