The best vaulters in the world run as fast as they can without compromising technique. They also make sure that they run the same way every time. Superior technique and consistency, coupled with whatever speed you have is the best approach. Compromising technique in an attempt to run harder and faster, will bite you in the butt. A great plant is only accomplished as a result of a great run.
Most people think that straight arms are the only sign of a good plant.
In actuality, a great plant is made possible through great body position. Your arms are an extension of your body. Throughout the plant, you not only want your arms up, but you want your chest, and body up as well. If your hands are up while you are leaning back or hunched over, you might run into some trouble, not to mention lower back problems. A great swing up can only occur after a great run and a great plant.