On escape maps fast zombies are the same speed as a regular zombie since Zero's last tweak.
The classes are what makes the game. You have to choose your poison, no pun intended. You can be fast and weak, slow and strong, or one of the middle of the road zombies. The poison can jump like a bitch, but is also the easiest to kill. Their knockback is insane, and they are sloooooooow. The one glitch I have noticed recently that could use tweaking, is the deformed on escape maps. they are as fast as a regular zombie, with no knockback, and mad HP. They still can barely make it on a box though.
When did Mikey become a Zombie mod pro?