1MB Image, I'll leave it as a link.
CPU Socket offset inside. All the boards have the RAM right beside the CPU keepout, so make sure the CPU cooler doesn't interfere with the RAM you're using. Just go by height.
The quick plus-points rundown:
ASUS Strix:
DDR4 up to 4333/4266
2x M.2 sockets; +2/3 via Hyper M.2 card
(anyone tried using the PCIe x4x4x4 mode for anything other than SSDs?)
USB-C Header
Temperature Probe Header
Asrock Fatal1ty
DDR4 up to 4333+(?)/4266
6 SATA 6G ports
PCIe x16 supports bifurcation to x8x8
Onboard Thunderbolt-C port on IO shield (TB3, USB 10GB, DP transport)
Chassis Intrusion Header
Heatpipe VRM and PCH heatsink
Asrock M-ITX
DDR4 up to 4000+/3866
6 SATA 6G ports
2x Gigabit Ethernet Ports
TPM header
1 DP and 2 HDMI onboard ports, Triple-Monitor capable
Chassis Intrusion Header
CPU socket closer towards top edge, so depending on build layout...
MSI GPC
DDR4 up to 4500/4400/4333
TPM Header
USB 10G on IO shield, 1x 3A 1x 3C
CORSAIR RGB HEADER (not Corsair Link controllable)
Gigabyte N Wifi
DDR4 up to 4400/4000/3866
2x M.2 sockets
1 DP and 2 HDMI onboard ports, Triple-Monitor capable
2x Gigabit Ethernet Ports
PCIe x16 supports bifurcation to x8x8
RGBW header
Regular Addressable RGB Lightstrip header, with Voltage selector jumper
I was actually thinking unraid & TB eGPU Would actually allow me to throw the really noisy and massive computer away my gf uses for gaming on...
that said, total sized and cost efficiency should point me down the matx route instead, but i really love my ncase m1. I've not seen any micro atx cases i'd want to swap that for (yet)