Intel Xeon E5-2660 @ 2.20GHz [dual cpu]
TDP = 95W, x2 = 190W
# cores 16 (2x8)
# thread 32 (2x16)
MAX Memory Size = 384 GB DDR3 1600
Max memory bandwidth per cpu = 51.2 GB/s (102.4GB/s)
PCI Express lanes = 40
Passmark score = 17,325
COST = $333.20
Intel Core i7-6700K @ 4.00GHz
TDP = 91W
# cores 4
# thread 8
MAX Memory Size = 64 GB DDR4-1866/2133, DDR3L-1333/1600 @ 1.35V
Max memory bandwidth per cpu = 34.1 GB/s (102.4GB/s)
PCI Express lanes = 16
Passmark score = 11,001
COST = $350
The dual cpu setup scored almost same as the newer Intel Core i7-6900K @ 3.20GHz (priced at $1100) and for much cheaper. You don't get built in gpu, older architecture, less instruction sets, doesn't support DDR4, and higher TDP when running dual cpu. But if plan don't plan on upgrading for awhile and would like to run SLI + great multitasking performance the Xeon seems like a no brainer when it comes to effective cost/performance unless I am missing something?
You may have answered your own question but I didn't see a model number of the motherboard you found to see whether it requires anything special like ECC memory or a special power supply. Also there seems to be multiple versions of the E5-2660
Intel Xeon E5-2660 v2 - Ivy Bridge
Intel Xeon E5-2660 v3 - Haswell-EP
Clock speed is lower on the Xeon I would suspect single core applications would be slower but some apps that use more cores it could be faster. Not sure where it falls with gaming.
You might consider selling the mobo it being a more specialty mobo it might command a price that will get you more on the i7 consumer line.
Intel Core i7-6700K @ 4.00GHz
Intel Xeon E5-2660 @ 2.20GHz
Passmark 11535 Single
Passmark 17325 Dual CPU
POV-RAY 653 (Single-threaded higher clock speeds will generate higher scores with this benchmark, so a dual CPU system does not help this benchmark much.)
As far as gaming goes this can do 4x SLI and I'm wondering if 4x GTX 1080 would even cause a bottleneck for this dual xeon setup. I'm not exactly willing to spend that much on graphics cards, but maybe 2 GTX 1070's, RX 480's, or GTX 1060's when they come out.
dont expect to get good mileage gaming on a xeon as it is made for servers and workstations.
with any game 4cores that are faster tend to do better having as many cores as you can throw at it. if you plan to do 4 way sli with 1080s expect little support from nvidia.
i would almost recommend 2 systems one for gaming the other for encoding as you can see the xeon scores better with x264 encoding but the i7 has far better single threaded performance and can be easily overclocked
UserBenchmarks: Game 27%, Desk 41%, Work 29%
CPU: Intel Core2 Quad Q9650 - 41.8%
GPU: Nvidia GTX 750 Ti - 26.6%
SSD: Intel Raid 0 Volume 240GB - 68.4%
HDD: Toshiba P300 2TB - 95.3%
RAM: Unknown 4x4GB - 23.2%
MBD: Dell OptiPlex 780
Beats my A6-5400k
UserBenchmarks: Game 21%, Desk 38%, Work 19%
CPU: AMD A6-5400K APU - 32.1%
GPU: Nvidia GTX 560 - 24.7%
HDD: Amd-raid Array 1 499GB - 89.8%
RAM: Unknown IM34GU48C16-999HB 2x4GB - 29.9%
MBD: Asrock FM2A88X-ITX+