GPU, VRAM, and VRM thermal sensor will signal system to lower speed if thermal limit met, you should only OC your graphic card with proper setup.
Raising MHz comes with the rise of wattage consumption, every cooler has its own TDP capability, problem is there's no exact math on how hot it'll become on # of wattage consume, not the mentioned that thermal sensors are within ~ 5 % error margin, so when you see 90 deg it actually ~95 deg or ~85 deg.
Limit GPU temp in afterburner to certain degree assured stable speed without have to throttle down,