8700K overheating?

[Backwoodsman]

I have a concern that my new i7 8700K based system, that is primarily used for flight simulation, is running too hot and would like opinions.

The system is:
Case: Corsair Obsidian 650D
PSU: Corsair AX760
Motherboard: ASUS PRIME_Z370-A
CPU: i7 870K unclocked
Ram: 16Gb DDR 4
GPU: EVGA GTX 970 4Gb
Cooling:
Corsair H100i Top mounted exhaust
120mm Rear fan input
200mm Front fan input

The CPU temperatures that I am getting are around:
30 degrees C - idle
65 - 70+ degrees C when running Prepar3d
Peaks as high as 86 degree C
All temps as per CPUID HWMonitor

A particular concern I have is that the H100i was standing around for about 6 months before it was first installed; could the the pre-applied thermal paste have gone off and lost its thermal effeciency?