Originally Posted by deltaboy37

A speedy zombie means less time to make decisions which raises not only intensity, but also shortens the reaction time available for proper decision making techniques. Any pressure situation requires special decision making skills and promotes the adoption of an intense contingency plan.

Slower zombies although scary can be toyed with and you can poosibly have all day to react, giving you precious time to decide whether to waste a bullet or walk over to that table 5 meters away and grab the crowbar. Fast zombies will cause you to waste bullets much faster.