I am currently running a dual display setup with nVidia 8800GTS video card, on a Ubuntu 12.10 box. The current setup uses nVidia TwinView to render the image on a 1920x1200 display and 1600x1200 one.

I'm planning to add a third, 1280x1024 display to the setup. The change will require me to upgrade my GFX card to one supporting triple displays. I'll probably go with Sapphire Radeon 7770 (FLEX edition, to avoid additional active DP->DVI adapters).

Before I invest in new GFX I wanted to ask - how well the AMD drivers will support such a setup. It does not matter whether it's fglrx or the OSS ones. If I remember correctly, when running Fedora on a Radeon x800, I had 'void' areas above and below the working area on my second display. The desktop was rendered in 1920+1280 width and 1200 height (which left 176px of vertical space accessible for my cursor and windows but not displayed on the screen - I'd prefer to avoid that). It may have very well been my misconfiguration back then. Generally, are there any solutions from AMD on par with TwinView? Or is it a non-issue at all?

Also, I'm wondering about the usual stuff - hardware h264 decoding support, glitch-free flash support, any issues with Compiz/Unity?