I was having similar problem recently but couldn't find any suitable feedback before buying new card.
I decided to give it a try and go for 4 x 23" screens setup with ATI FirePro™ 2460 Multi-View.
So far I've been playing with it for around a day and I have to admit I'm quite impressed.
Despite the fact that graphic card comes with 4 mini displayports and apparently require displayport screens to use it, this card comes with 4 displayports to DVI adapters and works fine with 4 DVI screens.
When I played sample video (quality isn't great - recorded using mobile phone), it was working well, even when displayed on all 4 screens. There was no tearing at all.
I configured all screens with krandtray - worked out of the box.
I'm using composited desktop and everything works surprisingly well (much better than on my old nVidia Quadro NVS 420).
Below you can find some logs.
screenshot playing video - 5.6MB
If you need any more information or logs, please poke me.
$ glxinfo | grep OpenGL
OpenGL vendor string: X.Org
OpenGL renderer string: Gallium 0.4 on AMD CEDAR
OpenGL version string: 2.1 Mesa 7.10.2
OpenGL shading language version string: 1.20