84C is the thermal limit, although if you are water cooling and hitting those temps the card sounds fudged. I have an MSI GTX 1080 Ti Gaming X Trio that doesnt even hit 60C when stress testing for 12 hours with an overclock of 2155mhz on core clock and mine is air cooled.
@80c GPU boost will become throttled. How many exhaust fans do you have? Is the GPU radiator using the cases warm air to cool itself, or it is getting cool air directly from outside the case?