Well, I had to build a 10k computer last month to stream in/out HD-SDI video, but honestly its pointless for gaming (especially since it has a quadro FX 3400 card in it, not a gaming card).
2xOpteron 280's = 1800
Tyan K8WE = 530
2 GB ECC Registered RAM PC 3200 = 400
Intel SRCS28X Raid controller = 530
11x Seagate 7200.9 160 GB HDD = 900 (8 for RAID 0 + 3 identical backup drives in case of failure)
1x WD 150 GB Raptor Boot Drive = 300
Dell 30 Inch Screen + Logitech Media Keyboard + Logitech G5 Mouse = 1800
2x Plextor DVD Burners = 150
PCP&C 1000W Power Supply = 460
1 Quaddro 3400 = 900
Lian-Li PC-201B Case = 280
AJA Xena HS = 900
Total: 8980. With overnight shipping it ended up being still less than 10k.
We eventually added an Aja HDP HD-SDI->DVI Converter and a 23 inch 1080p monitor for another 1900 dollars to preview our HD-SDI video on the Xena HS's output making it about 12k total. Also we added a $6000 h.264 hardware encoder to it, but that is more of a seperate expense.
Even while capturing 1080i 59.94 uncompressed video, compressing SDI video using the h.264 card and browswing the internet, I have yet to break 40% usage accross the 4 cores. Unless you have a reason to work with uncompressed video, massive multithreaded applications , or anything along those lines, do you really need to spend 10k on a computer, the short answer, NO.
With 5k you could build a beyond godly gaming rig around an FX-62 and 30 inch LCD, and then if you must build a conroe based one in 6 months with the other 5k. Even this I find silly, as I built my Opteron 170 Gaming computer for about 1750 shipped, and it dominates pretty much anything I throw at it (Including handling obvlion at 1280x1024 at over 60 FPS maxxed out)