+1 on carefully tweaking up the VCCIO and SA voltages. That seems to be mandatory for high speeds on DDR4. 1.25 for VCCIO and SA were what stabilized my system -- Maximus VIII Hero, I7 6700K 4.7GHz, G.Skill DDR4-3000 16GB dual-channel.
Try setting the "Maximus Tweak" option to "Mode 1". This relaxes the set timings slightly. At 3000MHz, even slight timing variances can have a huge effect and this seems to allow for some tolerance.
BIOS 1601 also seems to help. Can't put my finger on it, but overall stability and performance is just better.
Motherboard: Maximus VIII Hero
Processor: I7 6700K - 4.9GHz OC
CPU Cooler: Corsair H80i v2
Memory: G.Skill DDR4-3000 16GB
Graphics: EVGA GTX 1080 FTW2 1721/1860MHz
Storage #1: 1TB Western Digital Black
Storage #2: 2TB Western Digital Black
Case: Antec Nine Hundred
Power Supply: Antec Edge 650 80+ Gold
OS: Windows 10 Pro