Intel Motherboards : Can't get XMP to boot, long boot time

There is no 3000 MHz divider on the list, so I think it's not possible to set my RAMs at rated speed (3000 MHz) unless I could change BCLK which I can't because I have non K CPU.

But you set everything as I would do and this didn't work so either you had a huge bad luck or UEFI is still buggy as it probably is in my case. You may change only one setting in UEFI, it's at the bottom of DRAM configuration and it's called MRC Fastboot <- enable it (I have it enabled). My last advice would be to check RAM with Memtest86 to be absolutely sure it's OK. You may read my thread if you want just to see that nothing is certain with ASRock's UEFI  http://forum.asrock.com/forum_posts.asp%3FTID=4445&title=z270m-pro4-fast-boot-problem-and-no-temp-readings 

It is still new platform so I think it takes time to discover all problems and fix them. I'm curious if your new set will be free of flaws.