[heinzgruber]

I use a Flirc case (there is also a kodi branded version) that is very effective at removing heat.

You might want to try removing the case you have and aligning the PCB vertically to help with air flow.
Obviously a fan would be helpful (although not needed with a case like the flirc).

i use thje same case and my raspi3 overheats during amazon video and movies stutter. very annoying. running @1350 mhz. maybe my fault