Well given your clarifications, I have less faith in the above build as to suitability for your intended purposes.
Still, again, I'd wait if you want skylake to 1) let the bugs shake out and 2) because I haven't seen any interesting ITX / mATX MoBs as yet. My early forays with Z87 / Z97 boards certainly placed me on the bleeding edge, especially from Asus, did not go well as early steppings had issues with external drives not recovering from sleep and BIOS clock freeze issues.
And I should mention that most ITX / mATX solutions are gaming oriented for LAN party boxes. Not that that is a bad thing as a good gaming MoBo / GFX card for example is a great CAD MoBo / GFX card. However most workstation class boards are ATX ... so just how important is that small case ?
Will need some info as to the software used for for circuit analysis and its recommended system requirements in order to determine if it will benefit from the more workstation oriented.
So I will hold off on MoBo / CPU / RAM / GFX and give ya the following until such time as you can give some direction with regard to above:
PCPartPicker part list /
Price breakdown by merchant
CPU Cooler: Phanteks PH-TC14PE 78.1 CFM CPU Cooler ($64.99 @ Newegg)
Storage: Samsung 850 EVO-Series 120GB 2.5" Solid State Drive ($64.79 @ Amazon)
Storage: Seagate 2TB 3.5" 7200RPM Hybrid Internal Hard Drive ($89.88 @ OutletPC)
Case: Phanteks Enthoo EVOLV MicroATX Mini Tower Case ($129.99 @ Amazon)
Operating System: Microsoft Windows 7 Professional SP1 OEM (64-bit) ($133.89 @ OutletPC)
Total: $483.54
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-08-25 23:29 EDT-0400
The why's ....
-SSD for OS and critical applications ... SSHD cause it will load your data faster than anything else. It's about 50% faster than the WD Black.
-Cooler is best bang for the buck on the $50 - $75 range and has very attractive appearance.
-Case - Stunning looks and finish, and well the reviews / ratings say it all
http://www.hitechlegion.com/reviews/cases/44770-phanteks-evolv-atx-aluminum-case-review
-OS - Best thing about it, it's not Windows 10 or 8 but you can upgrade to 10 if you want and Pro version will let you delay force fed updates which could bring your engineering software to a halt. Been that, suffered that with AutoCAD.
Again, questions needed to hit the rest of the components:
1. Can you wait for the 2nd / 3rd steppings of CPU and MoBo to arrive and get you off the bleeding edge by waiting for debugged and performance tweaked components ? As we haven't seen them tested much, it remains to be seen which ones are the winners and losers. Mid November would be the time to plan fo Z170 allowing you to take advantage of these tweaks / improvements as well as Black Friday pricing. Read more on stepping and reasons to avoid the 1st ones here:
https://en.wikipedia.org/wiki/Stepping_level
2. How important is the small case ? I must say there are not many attractive offerings in the mATX class, at least not yet and not for your stated usage. There's not a one out yet that we would put in any of our workstations here in our engineering office.
Most mATX boards are gaming oriented and the sound solutions are also a bit weak for the most part ... would only matter if listening to music while working is a factor.
Among the larger boards, the Asus Z170 deluxe is one that fits the bill of a workstation class MoBo but at $320 cost is a bit steep tho not unexpected for what it delivers. The Gigabyte GA-Z170X-UD5 is another rugged board that looks promising at $190 as does the Asus 170-A at $165
3. When we do circuit design here for power and control in plant construction, it goes straight from brain to CAD but these designs are rather simple compared to what I imagine you are using.... integrated circuits ? Electronics ? If you could point to the software page, we could get a better idea of what your needs will be ?
-Does the software benefit from an increased number of CPU threads ? ... that will best determine the chipset platform and CPU choice.
-Does the software benefit from CUDA ? That will determine the GFX needs to a large extent.
-Does the software benefit any way from double precision or other aspects of workstation class GFX cards ?
-RAM whether DDR4 for Z170 / X99 or DDR3 for Z97 will definitely be high speed 2400 or above