The article mentions that you can't use FPS as a yardstick for performance if you're already getting "max", but there is a way around this.
You can measure the frame start and end time (duration) and divide 1000/average duration over 1 second. This will give you the render speed even if that's not the actual number of rendered frames.
You can measure the frame start and end time (duration) and divide 1000/average duration over 1 second. This will give you the render speed even if that's not the actual number of rendered frames.