The temperature of 85°C during a stress test is within acceptable limits for the i7-8700k CPU.
This temperature range is typical for the CPU during heavy workloads.
It's typical. The i7 already runs hot, and you're pushing it further with an overclock. The only solution would be to cut it down.
Absolutely typical. The only option is to disable the CPU.
Ideally fine when operating at that pace, it may overheat...