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Firstly, monitor your CPU temps whilst you are gaming and the slow downs I occur, I suspect you could potentially be thermal throttling. Especially as it is a mobile processor.
Secondly when your CPU reaches 100%, you are effectively limited by the capability of your CPU, so as a sanity check, just do the following:
- Ensure all drivers are up to date, including chipset (not using a driver updater app).
- Close all background processes and applications you do not need so you can dedicate resource to your game.
- Monitor CPU temps under load to ensure you are not thermal throttling.
- Change CPU based in-game settings to ease CPU usage.
Following that, it will likely simply be that your CPU has maxed...