80°C is for 6700K very normal. If the water temp equal or higher than you CPU Idle Temp, then it proofs that AIO is working good.
6th Generation 14 nanometer: i7 6700K / i5 6600K (TDP 91W / Idle 2W)
Tcase (CPU temp) = 64C
Tjunction (Core temp) = 69C
Tj Max (Throttle temp) = 100C
You have to undervolt your CPU.
1.15V at 4.0GHZ
1.2V at 4.2 GHZ
1.3V at 4.6GHZ
1.4V at 4.8GHz if Cpu is good.
Do not run your pc with BIOS standard Voltage. The Mainboard Manufacturers're set this higher than normal to guarentee that CPU works.
Do not benchmark SKYLAKE with Prime95, This is a heavy load.
I use a 6700K with ASUS z170 Sabertooth Mark 1. I have already a X79 System. First i installed my h100i, The Temps're very high. Then i installed the h100i in my older system with i7 3820. It was normal in Idle and in Load. Then I delided my 6700k. The temps are only 3-5°C lower. It didn't worht it.
Now I know
There are three reasons for this high temps
(1) Skylake is smaller then the older cpus. The 3rd and 4th Generation 22 nanometer Die, and the 5th and 6th Generation 14 nanometer Die have significantly less surface area in contact with the underside of the Integrated Heat Spreader (IHS), than the larger 2nd Generation 32 nanometer Die.
(2) 3rd through 6th Generation processors have more transistors packed into a smaller Die than 2nd Generation processors.
(3) 3rd through 6th Generation processors use Thermal Interface Material (TIM) between the top of the Die and the underside of the IHS. Solder, which has superior thermal transfer characteristics, was instead used in 2nd Generation and earlier processors, and is used in Intel's "High End Desktop Processors"
If you install Custom Loop Watercooling, don't be surprised if it is not cooler. The result will be the same. The Water in the Radiator has to be between 0-10°C to cool 6700k. U can try to put the radiator in an ice bucket without the Fans. It should work.
There is a guide for this temp problems:
P.S. Sorry for my bad EnglishEdited by Alperen62002 - 7/26/16 at 3:13pm