The problem with all these horizontal setups is that when looking at a screen for long periods of time, neck cricks are inevitable, and what's worse is that those cricks are just harbingers of future woe.

I strive to stay vertically and horizontally aligned to both my keyboard and my screen.

Even though I have a 1920x1080 monitor, I keep windows stacked in the center, and use multiple emacs frames rather than one frame C-x 3'd into multiple columns.

1440 pixels wide is about what I think is ideal at 1.5 feet of separation.