Best Foreground Application Response Time, the default tasking option, increases in a foreground application's priority two levels.
Neither foreground boost nor the heuristic priority adjustment will cause an application to change classes from normal to real time, or vice versa. The priority adjustment from these sources is bounded by the process class.
Foreground Application More Responsive than Background, the second tasking option, equates to a foreground boost of one level.
Foreground and Background Applications Equally Responsive, the third tasking option, deactivates any foreground boost. The SQL Server Setup program sets this during installation. This is mainly to prevent the database server from being CPU-starved by foreground applications and is the best setting for a dedicated SQL Server.