The X2 will help you A LOT when games based on Unreal Engine 3 start to roll out, unreal tournament 2007 is susposed to be out q1 or q2 of 2006, and the Unreal Engine 3 is multithreaded. You will get bitten in the ass later up the road if you don't get an X2. EDIT:
If you get an Opteron you will also have to get ECC ram with it, which is more expensive and slower than normal RAM.
If you get an Opteron you will also have to get ECC ram with it, which is more expensive and slower than normal RAM.