Getting the best gaming bang for the buck is smarter use of the money. SLI is probably the best recommendation with a MB that has dual PCI express. If you wait for friends at IWILL and Tyan, you will see some dual opteron 16x systems(real 16x, not a 4x with a 16x connector) in the coming months. Games like UT2004 benefit greatly according to Nvidia.
As others have told you, Opterons are designed to stable, and not allow for many of the tweaks that other platforms have. Also, given the nature of a dual graphics with SLI config, it is unclear how much more you would get out of it(BTW, it is nice to have a stable, non-OC'd systems every once in a while...).
While others have also quoted SCSI above, you can also consider doing a RAID 10(2 drives striped with a mirror and stripe set) of SATA-II drives. In particular, you are looking for both drive and controller to do a feature called TCQ(Tagged command queuing). The drive I know handle this well is the Western Digital Raptor 73GB 10K RPM. This drive is virtually as fast as SCSI in this configuration. These drives are also about $200 each, so the x4 array of them will give you a 146GB array with good read and write performance.
The Opteron 250's will set you back alot, so make sure you need it. Also, given that AMD is releasing a Dual CPU on one chip Opteron next year(it has been shown on HP's DL585 already), having a single processor may not be a problem in the long term(so long as it is an opteron(940 pin) slot).
Also, remember that some of the motherboards can use faster DDR2 memory
http://www.corsairmicro.com/corsair/xms2.html
Here is a config I am putting together, I am waiting for the Motherboard to be released from Tyan. The cost of the system below is about 6K, depending on the release price of the motherboard, plus another 1K for a 20" LCD Monitor.
Good luck with your purchase.
Lian Li V2000B Case
Antec Neopower 480 Power Supply
Tyan S2895 Dual PCI Express 16x, IEEE 1394b,USB2.0,Gb Ethernet
2 AMD 250 CPUs
2 Thermalright XP-120 CPU Coolers
2 120mm Globe fans, running at 5v mounted on CPU Cooler
Arctic Silver Ceramique - nonconductive
2 Nvidia 6800GT 256MB PCI Express Graphic boards ? PNY
1 NVidia SLI interconnect
4x512MB DDR2 400 or better RAM Motherboard certified, registered, ECC
4x73GB Western Digital raptor WD740-SD Enterprise 10Krpm
Configured 146GB RAID 10
1 Pioneer DVR-A07XLB DVD Writer ? Dual layer
1 Windows XP Pro
1 Novel Linux 9.1 Pro
Originally posted by: SneakyStuff
I noticed you put a link up for a motherboard with an AGP slot, but linked us to a graphics card which isn't AGP

My honest advice to you, if you have that much cash to burn, get a dual opteron motherboard, with dual PCI-EXPRESS X16 slots, and make use on nVidia's SLI technology (which = blazing fast, for a cost of course)
SLI