Z370 Extreme 4 Freezing, Very Frustrating!

Mobo: Z370 Extreme 4

CPU: 8700k (stock)

RAM: GSKill TridentZ RGB 16(8x2)Gb 3200 14-14-14-34 

GPU: Gaming X Trio 1080 Ti (also tested with integrated graphics and an HD 6870)

PSU: Seasonic Focus Plus Gold 850W (also tested with EVGA G2 750W)

SSD: Samsung 850 Evo 500 Gb.

When running at XMP frequency (3200), the computer always crashes a few minutes after loading into Windows, sometimes at POST.  Guaranteed instant crash when stopping a benchmark such as prime95.

I've tried every BIOS version, XMP/manual entry, bumping voltage to 1.4+, LLC 1, loosened timings, etc.  Can't get it stable at 3200 or 3100, but it will always work without issue as soon as I drop down to 3000.  I had initially suspected the RAM, but the  Z370 Extreme 4 is listed on the kit's QVL page, and after testing the sticks in a 7600k/Z270 Extreme 4, and running the full battery of tests, it would appear they do in fact work perfectly at the stated 3200 spec loaded through XMP or manual entry.

The whole reason I went with this board over a higher end one such as the Taichi or Gigabyte's Gaming 7 was because of the the rock solid stability I had gotten out of the Z270 Extreme 4.  So it's very disappointing to encounter this sort of issue!