The heal down technique might get you more speed in the short term, but it will sacrifice power. Power is what will make the drum speak the way that it needs to in order to give definition to your speed.
Play to a metronome. Every 5 minutes or so, when you are comfortable, raise the bpm a couple notches. Lather rinse repeat. When your legs get tired or start to hurt, take a breather. When you come back, lower the bpm to the last comfortable position. If you do this, with the heal up technique, you will gain the precision, stamina and sound that is needed for this sort of playing.