Click this link below to open an excellent Dell Support 'White-Paper' on your question:
Should also be able to download a pdf on that page.
My D800 as well as my new D830 are WUXGA 1920x1200 and that is by-far my preference.
The higher resolution (147ppi) screens exhibit far less 'pixelation' or blocky look when run at lower resolution,
(if you need to see something from across the room ).
Lower resolution can not display higher resolution at all, or will need to be 'scrolled around' but ppi will not change.