The harder you swing it, the stiffer you need the shaft to be because you want the shaft to stay in a controled flex throughout the swing. If you have a regular shaft and you are at 270, I would definatly go with the stiffer shaft. It maintains the accuracy with a higher swing speeds and as you know getting you more distance.

Just test them...as many as you can get you hands on. Get one you like to swing at 80% with and hit it straight. If you start to slice it, that is usually the sign you are too stiff and are not flexing the shaft enough. Don't pick the one that you have to swing 100% at to hit it straight...

Be patient about distance. It's not the deciding factor in you game...unless all you want to do is long driving.

Good drills for distance are:

1) Get you leading shoulder over your trailing knee in the backswing. Take a string and tape it to your shoulder. Without a club, just practice getting to this position slowly...this increases you flexability and increases the width of your arc. Hold that point where the string is on you knee for about 5 seconds. Do this over and over and over and over. Eventually, you should be able to be in this position while being in a complely relaxed state...not straining to stay there.