I was reading the System Builder Marathon, Sept. '09: $650 Gaming PC Article, and I noticed the graphics card, which uses a Crossfire configuration was no longer available.
Any 2 HD4850 in crossfire would have similar performance. I personally prefer single card solutions the HD4870 has a good price now and is very good up to 1920x1080 resolution, for little more money the new HD5770 can be had, new technology and almost as fast as hd4870.