Not that I've tried it, but dual 30" seems like it'd be a bit much for me. Or the OP's dream 50". There's only so much you can focus on at a time, and only so far you can turn your head to change focus, though I guess depending on what you do you might want more areas of focus. 3 window columns seems to be where I'm most comfortable, but I've never tried a display bigger than 1x30". I do keep a 'dashboard' on a smaller side monitor that I can turn to look at as necessary though.
You don't focus on everything at once. Secondary windows can be viewed peripherally -- for instance you can tail a log, and your peripheral vision will notice motion. The other benefit is multiple windows as an alternative to alt-tab. Moving your eyes slightly is a lot easier than pressing alt-tab -- it's can be done without concious thought, so it doesn't interrupt your "zone".
Interesting. I found I got a lot more productive when I switched from a large monitor with multiple windows to a smaller monitor with a single window switched via keyboard. And that was specifically because it was faster and required less thought to flip through windows than to remember where the window I wanted to look at was and to move my eyes to it.
However, I have poor eyesight and very poor peripheral vision, so that might have something to do with it. If I'm trying to watch for movement out of the corner of my eye I frequently get false positives from visual aberrations.
