Hey community! I just wanted to let you guys know:
With the new driver, power throttle and Wattman crash issues are fixed. I don't have power throttle related clock speed drops anymore. My Sapphire RX 480 Nitro+ 8gb OC runs cooler than before and it consumes approximately 15 Watt less power with increased in game performance. And I don't need to change any power limit settings to use full power of my gpu.
Moreover, Wattman does not crash anymore when I try to open it and it is completely stable.