I would get the 5600 becuse I dont beleave the 4800 supports DX9.0, and if you are looking foreward to Halflife you really want DX9.0 support because it will be a DX9.0 game. Also grab the one with 256 meg ram onboard, you can never have enough ram. Also if your gonna do video editing I would get something with Vivo and a video capture chip.
Gainward makes Great Cards by far with the most bang for your buck! They usually always include a video capture chip and Vivo and dual monitors.
http://www.gainward.com/