I didn't like ASRock Z170 Gaming-ITX and I've returned it. It cost ~20% more than MSI while was offering less and was overclocking worse. I guess that Z270 is better as in specs are higher clocks etc.
I was benching MSI Z170I Gaming AC on dice and SS and I had no issues except it had vcore at max 1.52V so I stuck at ~5.4GHz. Still everything else was overclocking great and I was in top 3 in some competitions vs guys with ASRock OCF. Last 2 generations of MSI boards are really good. I have Z270 Gaming Pro Carbon and everything works without issues. 7700K runs at 5.2GHz+ so it's not bad.
Recently I'm almost only buying and recommending ASRock and MSI. I didn't like last ASUS Maximus series but I wish to check Strix ITX. I'm not sure if I decide to buy it as it won't be cheap.
I'm a sicker for RGB lighting. The new g skill 3200 16 GB set released today with the RGB lighting headsinks. 14CL I'm thinking it'll pair well with the z270 by ASRock. Ivr heard ASRock plays well with a wide range of ram.
Depends what do you expect. Lower ITX will support DDR4-3733 max and that's only in single channel. I would trust what ASRock says as the same was with Z170 which was supporting memory exactly as high as they said.
MSI Z270 Carbon is the only one from the list ( except Strix which isn't available ) which has RGB lighting and you can control modes via soft. It's also one of 2 motherboards with declared DDR4-4000+ support in dual channel ( other one is Strix ).
Every motherboard mentioned in this thread will work at DDR4-3600 or below in dual channel. I also had no issues with any ASRock or MSI motherboard and memory compatibility. Once was issue with new Hynix IC but I got beta BIOS from MSI which was fixing it ( it was memory profile issue and ASRock confirmed that too ).
Btw. if I'm right ( and my contact wasn't lying ) Trident Z RGB isn't officially out yet. For some reason it's listed in some stores and first delivery will be in couple of days. Actually I ordered 3866 kit but I haven't got confirmation yet if they accepted my order.