This has to be the most ergonomically inefficient set-up ever! I also cannot fathom how to work with 21" at least). And a tiling window manager. And a decent mechanical keyboard... ok ok.. Interesting setup. I'd be interested in knowing how it works out in the long term.
The screen is just the right size to fit two 80x25 text editor windows side-by-side when full-screened. Swiping back and forth with Mission Control is almost as quick as switching your glance from one big monitor to another. Having your "mouse" right below your keyboard makes clicking something only marginally more time consuming than contorting your hands to hit an Emacs command sequence.
Probably still faster with the big setup, but I get a lot of mileage out of my little setup and I get a huge productivity/creativity boost from being able to wander around the house, head to a Starbucks, etc.