As you have been able to notice from my reviews, the X299 platform has massive challenges in overclocking (and other segments as well). Pro-overclocker Der8auer now states that the X299 Platform a “Disaster” for tweaking. 

Der8auer voices his take on X299 on his YouTube channel and focuses mostly on the poor state of MOSFETs / VRM versus cooling. Der8auer mentions that the temperatures are running too hot under load. Measuring the front and the back of his AORUS X299 Gaming 3 board, the temperatures read 84.2 and 105.9 degrees Celsius. The heatsinks on the motherboards apparently are not enough to keep the MOSFET temperatures in line He also mentions that his ASUS X299 Prime motherboard shows even worse numbers.

These values are only at 4.6GHz at 1.2V, which is extremely mild for an overclock. He spotted 105.9 degrees. Der8auer mentions these values are reached after 15 minutes of Prime95 with a non-AVX load. If he used a CPU stress program that actually uses AVX, the temperatures will be even higher.

 
Der8auer states all current motherboards are poorly designed for overclocking. He states Skylake-X CPUs are drawing too much for only a single 8-pin feed. This results in higher temperatures and can even burn some power supply cables. Such temperatures can climb up to 80 or 90C, which is dangerous. That is why according to him, he cannot recommend ANY X299 motherboard with only a single 8-pin PSU connector (mind you that only applies if you plan to overclock).

It does not matter whether it is Gigabyte, ASUS, ASRock, MSI, etc. No matter how good the VRM design claim is, if it only has an 8-pin power connector feeding the CPU, stay away from it, Der8auer states.

Pro Overclocker Der8auer Feels X299 is a Platform Disaster for Overclocking