It is a fine build.
ROG R5E10 is basically the last and arguably the best X99 motherboard. The competition has some nice X99 offerings as well, but the R5E10 is a worthy successor to ROG's "flagship" R5E which held its own in the top-tier since X99's beginning. You would not be disappointed with an R5E10 (or with the ton of accessories it comes with).
i7-6950X is basically the best overall Broadwell-E LGA2011-3 processor.
There are a few
Haswell-E Core i7(-K) processors and
Broadwell-E Core i7(-K) processors with more speed but less cores/etc. There are many
Haswell-EP Xeon (E5-16xx-3, E5-26xx-3) processors and
Broadwell-EP Xeon (E5-16xx-4, E5-26xx-4) processors with (lots) more cores or (some) more speed, etc.
They all use the same (22nm/14nm) process lithographies, they all have the same 140W TDP upper limit, they're all binned/configured/priced off the same handful of silicon dies - so there's always tradeoffs where more of something means less of something else.
(All of the "non-X" Core i7 parts and Xeon E5 parts can indeed be overclocked on these mobos, in case you're wondering. Check my system specs.)
Processors on Intel's new X299 platforms will use LGA2066 socket, NOT compatible with X99 platform LGA2011-3 socket.
Intel's "leaked" roadmaps scheduled the X299/LGA2066 launch for June/July 2017 - less than two months away! - and rumours abound that they've "rushed" the launch in response to AMD swooping back into the market. Skylake-X and Kaby Lake-X Engineering/Media samples have already been distributed, reviewers are already running these parts.
So you can buy X99/LGA2011-3 (which is now a more "mature", stable, proven, and somewhat less costly platform) or you can buy X299/LGA2066 (which will equal or exceed "old" X99 in every capacity, support more new features/compatibility/technologies, cost more, and - as usual - be somewhat buggy throughout most of the first year). And don't forget about AMD's powerful new
Ryzen AM4 X370 (and upcoming
AM4 X390/X399) "HEDT" counterparts!
The newer (X299/AM4) platforms promise greatest longevity. X99 is still "new" but it's been around since mid-2014 and is already one step closer to EOL "legacy" obsolescence - although it's already massively overkill for many years of hard computing. Make sure you get a robust (even overkill) PSU and CPU cooler if you want to maximize your system's longevity.
The advantages of "HEDT" platforms are multicore megathreading madness, much higher (DDR4) multi-channel memory bandwidths, and greater number of PCIe3 lanes (along with greater motherboard bus bandwidths to transfer tons of data to-and-from processing components). The sort of stuff you'll need to maximize performance on *heavy* lifting and crunching productivity software (CAD, Autodesk, MATLAB, SPICE, SIMUL8, etc). A GTX1080Ti is a beast for FP32/FP16 work, but not so great at FP64 - neither is Titan Xp, sadly - so if you need lots of DPFP-based parallel/render computing tasks which lean heavily on GPU (GPGPU, CUDA, PhysX, etc) then you'll need to get a proper workstation card (I used a Tesla K80 GPU-A for 18 months) and you'll need to pair it with big/fast RAM and storage to minimize data bottlenecks and maximize performance efficiencies.
The advantages of "Performance" and "Mainstream" platforms are (much) lower cost and (some) greater compatibility. A fast 4C/8T 8MB CPU is more than adequate to run today's most demanding game/software titles, and it should continue to remain adequate for many years Same for, say, 16GB to 64GB of fast DDR4. And for the mighty GPU cards (like GTX1080Ti), albeit they'll look much less impressive in just a couple years.
This is basically the "baseline" platform spec targeted by devs so games/software will (increasingly) be code-optimized to run on it (while incidentally also tend to not run any better/faster on HEDT hardware they're not code-optimized for). Intel Z270 and i7-7700K (or AMD X370 and R7-1800X) are already overkill for 99% of real-world computing, and a GTX1080Ti is basically capable of >60fps 4K gaming - at a much lower price than your X99 build.
It always boils down to the same two questions: what do you want/need your computer to do and how much do you plan to pay for it?
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