I know from some Zombots servers, that they are lagging, because the Zombies change every 0.5 secounds (or fewer) their models.
And there are 5 (or more) models for a zombie per secound (so that looks like an animation) and there are exist 25 zombies.
So that means, that every 3 secounds have changed 125 models (or fewer, I don't know, but very much).