I personally have both a 4800+ system, and a dual opteron 252 system. Technically they should operate the same due to core speeds being the same and the like, but they simply dont.
The opteron can encode a full DVD to xvid in about an hour and a quarter (two pass, ac3), the x2 takes almost two hours, sometimes more.
Here are the reasons for that.
1) With a dual opteron you get two independant memory controllers, hence, double the memory BW
2) With a dually system you can get NUMA, thus increasing your memory bw even more, and boosting performance incredibly
3) The hypertranport chain used between two 2xx level opteron is double the bw of that used internally within the X2
In short, for video editing alone, a dual opteron box destroys an X2 system.
As for a recommendation of hardware, definately go with the Supermicro H8DCE for a motherboard. Its far superior to the K8WE that everyone raves about (ive used both). And then be sure to choose troy core opterons, as the SSE3 is a crucial element in most encoding programs.
This also leaves better upgrade possibilities as he could upgrade to two dualcore opterons at a later date, thus essentially having a 4 CPU box.
Let me make this clear, i am not advocating dual opterons for everyone, for the casual user or gamer, an X2 is a far better choice. However, for video editing opterons are untouchable.
