I've made this post just to share my findings.
Tested a i5 7500 with a Gigabyte H110M-S2HP and a pair of PC2400 memory sticks.
Original BIOS (F4): no boot
Updated with Skylake CPU to F20: boot with the memory running at 2400Mhz.
Runs stable with no issues whatsoever.
Funny how this H110 motherboard has no issue running the memory at 2400Mhz for which it never was advertised. It's a sad thing how Intel limits the memory speed on these boards.