I'll avoid asking the obvious "why?"...
If you want the fastest it can technically get without messing with different motors or whatever you'll need to fly it in fully manual mode. Wind speed is a key component. According to my Flytrex readouts I've had it going along at a smidge under 60mph with a tailwind, and that was in GPS mode.
There comes a point though where you can't tip it over any more without losing lift so there is a limit to how much lateral thrust you can generate and therefore your top speed. Plus of course the faster you go, the more quickly you need to turn it around and bring it back...
Taking the camera and gimbal off will probably squeeze a bit more out of it due to reducing the wind resistance.