No you do not have to be parallel at the top. In fact, I would suggest shortening your golfswing to 3/4 backswing. When I played on the college circuit, I am not sure if I ever saw a swing hit parallel at the top. Except for this one bloke who enlisted the John Daly technique and sprayed the ball all over the place.
I am a firm believer, like Leadbetter, that power comes from lag, not the length of the backswing. Look at Tiger, Sergio, Michael Campbell - all short backwings. More control. If you want power, enlist some lag drills like hitting 3/4 knock down shots. You'll be surprised just how far they carry.