A stiffer shaft does NOT necessarily mean "more accurate". The important part is to find a shaft which fits YOUR swing. Get a shaft which is too stiff and you will lose distance and accuracy.
The stiffness of the shaft, and where it bends (called the kickpoint) is dependent upon several factors of the player, including swing speed, and transition quickness. Just because a player has a fast swing speed does not automatically mean they should use a stiffer shaft. HOW the transition occurs from back swing to down swing is just as important as the top speed of the swing (if not more important).
In addition, "stiffness" is a non-standard spec between manufacturers. There is, in fact, no way to compare shafts just by the "stiffness" label on a shaft.