Will be running 3DS Max with Brazil v2 on 64-Bit Win 7, and want fast rendering as my primary focus. Looking at 2 system options that have been recommended to me, and want to make the best decision for the money:
For the dual-Xeon, you need more than 6GB of ram because there are 8 or more ram slots with at least 4 PER cpu. So, you need an even amount of ram for both CPUs. At a minimum, you should get 2 6GB kits because the Xeons are triple channel. For best performance, each CPU needs a multiple of 3 ram slots used for triple channel. Furthermore, because this will be a workstation, 12GB of ram will provide much better performance.
Now that I looked at that SuperMicro motherboard, it has only 6 total slots for ram. If 12GB of ram is not within your budget, look at 2 4GB sticks which tend to run $125 each. It won't be triple channel but you will at least have 8GB of ram and can easily add more later.
As far as I know, all high end 3D software can't use SLI or Xfire. I only know of nvidia's Quadro being able to 'team' 2 GPUs for rendering but it doesn't use SLI for it.
For hard drives, the sweet spot is 1TB mainly because the platters are 500GB each and a 750GB is essentially a 1TB drive with less space available. Also, I believe the 1TB drives are only slightly more($10). 500GB drives are $60, 750GB are $80 and 1TB are $90.
For Power Supply: a 650w will be enough unless you add 5+ drives and/or high end graphics card later on. The PC Power & Cooling 750w is one of the best along with SeaSonic and Corsair.
You can't go wrong with the dual Xeon 5520. It is far faster than dual Opterons and only a dual 6-core Opteron can keep up with the Xeons but those Opterons are $1000+ each.
Do you already have a case? I ask because these dual-CPU motherboards require a larger case that can fit an E-ATX motherboard.
The only other thing you will need is a Molex to 8 pin CPU power plug($5).
To save some money, what about a 9800GT 1GB for aound $100.