Check the distance to the destination. If it is under ~4,000ls, divide by 6 to find the fastest speed that won't cause you to overshoot. Disengage SCO when you hit that speed and you will never overshoot. Given the acceleration curves, there is always a chance you will undershoot (this approach basically guarantees it), but you can always switch between 100% and 75% on the throttle to compensate. It's not (usually) a bad thing if you overshoot your speed target, provided your throttle is at 0%.