Motherboard upgrade?

[Gammagoat]

I currently have a Asrock z170 pro4s and have my 6600k overclocked to 4.5 @ 1.355 vcore(1.344 shown in HWiNFO64). This has passed 8 hrs of Realbench. However things are different with OCCT and IBT, they both fail on large data sets and max respectively. The computer does not bsod, crash, but I am getting some new artifacts while gaming(shadows of mordor and the witcher 3)

The board vcore droops from 1.344 to 1.280 under load. I have set LLC to level 1 which I believe is the highest setting on my board, this has zero effect. I cannot disable turbo boost and change the multi so this has been left on, all c-states are off as is speed step.

I have the installed latest bios and drivers, no change.

Temps are good @ low 70's in IBT.

My complete setup,
Asrock z170pro4s
6600K
G,Skill Ripjaws ddr4 2400 XMP profile set.
850 Pro ssd
EVGA 650 P2
NH-D15S cooler
Gigabyte G1 1070


I have a feeling that my cpu has more in it, but I am not sure what motherboard will be best to buy?

I have narrowed to choices to the following four boards,

EVGA Z170 CLASSIFIED

ASUS MAXIMUS VIII HERO

ASROCK OC FORMULA

ASROCK EXTREME 7+


M2 storage is definitely in my future and possibly SLI once I've learned some more about it, but what I am really after is a board that will be great not only for gaming but also high OC capability and bench marking.

Are there any real differences between a board that is geared towards overclocking and gaming?

[Bananasplit_00]

overclocking boards might have more power phases and more precise voltage controll but the only "overclocking board" that you have there is from ASRock and i wouldent count on it beeing amazing but look at the specs, my 4690K is at 4.5Ghz @ 1.333V and goes up to 80C when stresstesting so a new cooler is something i need if i want to go any higher in the summer(its 4.7Ghz in the winter lol)