If the settings not help, something I saw more then one time, deinstall Sophos to test if it is the culprit.
You can reinstall it afterwards.
Please preform a clean boot and test the Game in clean boot mode.
Make sure your virus scanner and other security software and also Afterburner and similar software is disabled.
Make also sure that your GPU & CPU are not overclocked.
Sophos has a page on this, don't uninstall it that is just poor advice, add exclusions in for affected program, be patient for your local install to update,
below link has number of games that don't play nice/act lick viruses and need additional exclusions to allow them to run.
