In case you didn't see my last post in your original thread, I went into more detail about Puget Custom Computers and Tantus Computers. That post is on p. 7 of that thread.
In the beginning, you said you wanted to get away from Dell. May I ask why? Were you dissatisfied? If so, I recommend trusting yourself and consider other vendors. I think Dell has something like a 4.5 lifetime rating over at Reseller Ratings. Pretty abysmal. I realize those ratings don't tell the whole story, but still, I think they're valuable.
Anyway, here's what I configured over at Puget Custom Computers based on what you said you want and using your Dell configuration as a model. You can find Puget at http://www.pugetsystems.com
Motherboard: Asus NCT-D Dual Xeon 800 DDR2-400
CPUs: Dual Intel Pentium4 Xeon 3.2GHz 800FSB w/ EM64T
CPU Cooling: 2 x SwiftTek Quiet Fan (for Xeon)
RAM: 2GB OCZ DDR2-400 REG ECC (2 Sticks, 2x1GB)
Case: SilverStone TJ05 (Black, no window) (Has 120mm fans front and rear; option to use 2 side 80mm fans for extra cooling)
Power Supply: Sparkle 460W Dual Xeon 24-pin Power Supply
Hard Drive 1: Western Digital Raptor SATA 74GB 10,000rpm
Hard Drive 2: Western Digital SATA 250GB 7,2000rpm
Video Card: EVGA GeForceFX 6600GT 128MB PCI-E
Optical Drive 1: Lite On 16X Dual Layer DVD+RW/-RW
Optical Drive 2: Lite On 52x/32x/52x CDRW
Operating System: Windows XP Pro SP2
Extended 3 Year Warranty
Case Mods: Round IDE Cable (for optical drives)
Additional Cooling: Arctic Silver V Thermal Compound
System Price: $3,776.14
In contrast to the Dell system you configured, at Puget, you know the brand of motherboard (ASUS) and the exact specs; the brand of RAM (OCZ) and exact specs; and so on down the line. I tacked on a 3-year warranty, but I didn't know if you'd want that. And you could always choose a different case, different power supply, etc. You just tell Puget what you want, and they'll get it for you. You have far fewer customization options at Dell, IMO. Also, Puget doesn't outsource their warranty. So, if you ever need tech support, you talk to the people you dealt with in the first place. If you want to talk with the owner of Puget, Jon Bach, he'll be happy to assist you. I doubt if you'll be able to chat with Michael Dell. At Puget (or one of the other top-ranked custom PC vendors), you get high-quality components and excellent customer service at a reasonable price -- at least in my opinion. In terms of value, I think you need to factor in customer service. Since this will be a mission critical rig for you, I think you'd be better served by a company like Puget.
Just my two cents.