But as a long time two display sidebyside user, the main function palettes - things with numbers and the info box, should remain close to the floor plan view. Less immediate things can be offset, but you'll see that having a full plan window on one display exclusively can be hard on the eyes.
I put the immediate palettes at the top of the main display, above the floor plan. Remember, I'm fifty, and while I can still kick, shimmy and strut, my continuously variable glasses reduce peripheral vision - lot of head turning now.
But that is a 21" solution - In future, when the 30" displays arrive, I'll probably put them in an over/under configuration - works fine if you detach the keyboard and have no desk surface directly in front - with a full floor plan above and palettes at the top edge of the bottom display. This will be great for longitudinal sections.
I see a captain's chair with wireless keyboard telephone and mouse sitting in front of this huge surface that descends below a typical desk height.
If you are getting smaller displays - say 17" - and plan to work side by side, it is much easier to see everything at once than with 21"....
Dwight Atkinson