Hi. Thank you all for sharing your observations. I'll be back this evening, and say something about why I am scoping a machine of that size/speed/etc.
Here's an example of one. http://outlet.us.dell.com/ArbOnlineSales/Online/SecondaryInventorySearch.aspx?c=us&cs=28&l=en&s=dfb&sign=PXhcOSHtr1T4IOw/PR7Uda1Mtc8wRStEeSXSEJCGYVjTuPd8Rly2S/x+KAw89DLAXfv3SzQZ0soZPA7YZIibEe9jGi6DTDcUgQAkNLuEXQ0V/bLM38jhq8k+osRUnB1FMy6ss5Un1KJu5igAHuqLn7N1g4ZJ2LZl4yDHbsT3vmxB9QfUuBGo80xH3obEypDh If you're going to run 4k monitors, you'll need an appropriate video card... like an NVS 510. (There apparently aren't all that many video cards which can display 4k res... most that can display more than one monitor are quads... and the text will be very small, requiring you to adjust the font to larger size. You might check out the 2560x1440 res monitors.... much more in the way of video cards to choose from.) Dell Precision is a "business line" class of machine and gets better tech support (excellent, BTW, in my experience) than their retail lines. HP has a workstation line which specs almost identically to Dell Precision (both mobos made by Foxconn and perhaps even identical?).... but the HP is at a higher price.
In the T5810, you'll want to go with the E5-1620*. It's 4-core, dual thread. The E5-1603/1607 are 4 core but not dual threaded.... and run on slower RAM. The 1620 costs more but benches ~90% higher than the 1603. However, if you're buying from Outlet, you can watch to see when a 1620 unit is well priced for about the same as the 1603/1607. And don't be afraid of "scratch and dent" models. (It's not like the side is caved in or anything.) I got one once which had a small scratch on the top... which was painted black... I just colored it over with a black magic marker and never noticed it again. I got another one and could hardly even find the dent.... a very small one on the bottom edge of the case. For accepting a "S&D" unit, Dell prices it about $60-$100 lower. Good luck. *It also has an E5-1650 CPU as one of the options. It's 6-core, dual thread. Newegg has sold those used off 3-year lease in the HP variety (Z420)... for ~$400. If I were in the market right now for a trading rig, I'd buy the used HP. Virtually identical specs to Dell's.
Bring SSD's for everything you may have, I would say totally remove SATA ones and go straight for PCI-E 4x and be sure your motherboard totally support that mode, cause lof of times they are basically something like PCI-E 1x and that's really that.