Easy to reproduce, just hit "Play" from Steam launcher to get stutter, hit "Safe" to get smooth.  Game has not had issues on this hardware before.

Using a Dell S2716DG GSync 2560,1440 display, just upgraded to 32G RAM (4x Corsair CMK16GX4M2B3000C15)

• Name Intel Core i7 7700K
• Codename Kaby Lake
• Specification Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz
• Mainboard Model PRIME Z270-AR
• Name NVIDIA GeForce GTX 1070
• Board Manufacturer ASUSTeK Computer Inc.
• Revision A1
• Codename GP104
• Core family 0x134 (GP104)
• Technology 16 nm
• Memory size 8 GB
• Memory type GDDR5
• Memory vendor Micron

Settings.ini:

[General]

IniVersion=23

VendorID=4318

DeviceID=7041

[System]

FullScreen=0

Resolution=2560,1440

Api=dx12

VSync=0

HotLoadEnabled=0

UIScale=1.3

Does it stutter in graphics APIs other than DX12 as well? I know it's a pain but can you confirm you've gone through all of the steps here as well.

That's very helpful info!

430.64 installed and worked fine.  I found 430.39 was not a problem after unchecking, then re-checking GSync.

430.64 I found I can cause to stutter using Alt-Tab to Windows, then back to Ashes.  No issue with Alt-Tab if I leave G-Sync unchecked.

Mostly a curiosity at this point, except knowing I don't dare Alt-Tab in game because I didn't pony up for the G-Sync video card and monitor to leave it off.