Differences between the 2 FGLRX graphics drivers

The 'post release updates' will install Catalyst 11.9 which is the latest version while the 'ATI/AMD proprietary FGLRX graphics driver' will install Catalyst 11.8 which was the driver at the freeze stage of 11.10 development

There has been issues with the 11.9 driver with Unity (see ubuntu forums here) so I suggest you install the 'ATI/AMD proprietary FGLRX graphics driver'.

there is a problem with fglrx and unity involving vsync. open up "amd catalyst control center", then head to 3D/more settings and set wait for vertical refresh to always off. this should speed things up a huge amount.