I am reminded of a horror thought I had when I was a child, by which I mean, when I was a child, I had a traumatic imaginary life. Iíd be terrified of nightmares, and when I had them, they were the stuff of Hell. This one thought I had was about being chased around my house by some evil old man, looking somewhat like a zombie. I donít recall exactly what this person looked like, but the focus of my thought was about speed. And the strange thing was that it seemed scarier if the evil person was slower. Why? I think it might be because if the evil entity is slower, it gives you more opportunity to escape, thus creating more tension because it becomes your responsibility to effectively flee, or fail to flee. A faster creature would get to you in an instant, and there wouldnít be much tension in that, and on top of that, there wouldnít be much time to feel this tension. Thus, a weaker creature is not necessarily less scary. Think of zombies! The slowness of zombies is usually counter-parted by their number. If you had just one slow zombie, itíd make for a pretty ridiculous story, but when you have hundreds, it works. If those hordes of zombies were extra fast and efficient, youíd have your characters killed in about twelve seconds. Not recommended, unless your characters have some weapons or situation that counter-balances that. Itís all about balance and tension.