When you installed the driver, did you do
? That initializes all of your cards in xorg.conf.
sudo aticonfig --adapter=all --initial
The driver in the Ubuntu repo is 12.4 and is the offical 12.4 ATI driver. The current ATI driver is 12.8. The problem with installing from the ATI website is that if the kernel is updated during your normal Ubuntu updates, you have to reinstall the driver. Using the one in the repo does not require a reinstallation.
Also, the fglrx-updates (called Post Release Update in the GUI, I believe) often does not work, so I would avoid it.