How can one run too fast? Speed is all that matters!!
On a more serious note, using SHIFT/A/RIGHT ARROW You can actually slow down. We took into consideration that the insane speeds are a bit absurd sometimes and makes for unavoidable damage. As for the differentiating zombies, what'd you mean? As in different models for the zombies, or making them stick out more as things you need to avoid? If the latter, we are already working on that.