For 2D one screen takes 4 bytes (RGBA) * (2560 + 1200) * 1600 = 24 MB.
A 8800 GT with 512 MB RAM should be just fine to handle this and still have room for back buffers etc. Under Windows 7 or Linux with UNROTATED displays, it definitely is.
That's why I asked in the AMD section of the forum: does a setup like mine work good in 2D (3D/compiz would be nice to have) on AMD? As I may add my 3rd TFT to this display group AMD is also my first option compared to adding a 2nd NVidia card.