[to3m]

DPI would be more of an issue than screen size, I think. I've got 2 portrait (1200x1920) 24" monitors side by side, one in front of me and one to the right: 28" wide, 22" high, for a 35" diagonal. It looks like this: http://quadruple-a.com/2_portrait_monitors.jpg

I find this works well, and isn't too overpowering. A 35"x23" arrangement would surely be no problem in terms of overall size - but you would be squeezing 1.8x as many pixels into rather less than 1.8x the space. Not sure my favourite 6x13 xterm font would look so good any more...

(I also tried adding a 3rd identical monitor on the left (total 42" wide, 22" high, 47" diagonal), and this looked perfectly manageable. So I'd probably be able to handle a 50" monitor... maybe. 3 monitors all lined up was starting to look a bit intimidating. And in the end Linux wouldn't display anything on the 3rd monitor anyway, so what it would actually be like in practice, I couldn't say.)