The subject of the beta 4.9 and official 4.8 have been touched upon by the person named 'Catalyst Maker' on the Rage3D forums. He helps with the creation of the catalyst drivers. He said the 4.9 beta are more up to date than the official 4.8. They just didn't have to go through the WHQL certification yet. So if you want the most up to date drivers, go with the beta 4.9s. If you want the most up to date certified drivers, stick with the official 4.8. I'm gonna stick with beta 4.9s for now until the official 4.9 drivers are released next month.
Link to beta 4.9:
http://www.ati.com/support/infobase/4547.html