two 560's would be enough yes, I can't stand 720p for desktop use, gaming however it isn't AS bad.
I use a 32" 720p TV as a monitor. I sit about 4' away, so the pixel size is not an issue, but it's very difficult to use for work (coding) because of the limited desktop area visible.
Games are fine, all modern games are programmed with 1360x768 in mind, so UI etc are completely fine. One advantage is frame rates are great!
I plan on upgrading to a 1080p 120hz display as soon as the 27" versions show up. But I know I'll need to buy and maintain a higher-cost GPU, as I'm doubling the pixel count.
I really like the idea of a 2560x1440 display that I could use for my desktop, and then pixel double and get the good frame-rates in games. But I want 120hz more... Wish I could have both!