If you would prefer lower temperature, most likely need to reduce core clock turbo value, eg reduce core clock value to 35 instead of 39. This can be done through throttle stop but not in XTU. For my case without re-pasting, I reduced my all core clock to 32 and temperature always maintain around 75-80C (full load).

yes it will reduce clock speed and impact minimal FPS in game. Since those AAA games utilize graphic more than processor.

Normal usage mean web browsing, documentary stuff, watch youtube? These usage will not affect much but 3D rendering and video editing will have slight impact - longer time to process.