I'm going to go with 3x2 is bad for the same reason 2x1 is bad, split right down the middle.. heck I saw a 3x2 review recently and they kept badmouthing the idea because pretty much everything important is drawn in the middle (well and they turned on bezel 'correction' which means they couldn't see anything in the middle).
http://www.pcpro.co.uk/blogs/2010/02/25/ati-eyefinity-on-six-screens-first-look-review/
PCPro takes a look at the 3x2 -- no video, just screenshots (of Race Driver: GRID) and text. They had bezel correction on and their chief complaint was things in the middle disappearing making it discard vital information.
Now personally I believe it's their own fault for having bezel correction on, I always leave it off because of precisely this reason.. but who knows I've previously played FPSes at a competitive level so missing even a few pixels would be vital. Though who knows I may just try it one of these days since I only play casually now, the only other thing is rendering extra pixels = worse performance.