I'm considering a three screen set up and have both 16:10 and 4:3 screens but I have no experiences with Eyefinity.
What I was thinking of was setting up with a 24" 19:10 screen in the centre and a pair of 20" 4:3 screen at the sides for 1600x1200 -1920x1200 - 1600x1200
Or buying a Dell 3008 and turning the two 20" screens in portrait for 1200x1600 - 2560x1600 - 1200x1600.
Cheers.