I always thought the variety of zombies was off-putting. Like 12 zombie nurses or other named zombies, it just seemed.. cheesy? I've been thinking it would be nice for a bunch of decrypted zombies such as the ones you see from black-ops 1 and 2 zombie modes; I prefer to have zounds of massively-disfigured and unrecognizable zombies swarming me than 7 nurses, 5 darlenes, a few cops and 4 or 5 zombie steves and etc. Horde nights I definitely see the need for boss zombies -- maybe they lead the army to you or something? Or charge the front and be a bullet-sponge wreaking ball to bust through the initial walls/defense for the horde behind them. I always thought the cops were just a bit too much cheese mode, yelling "OWWWWWWWWWW" or whatever when you hit them then spitting vomit at you lol. (speaking of, I don't think zombies would feel pain so, to me, pain reactions are weird).
On the performance of a few variate-zombies VS a mass, I think having a ton of slightly identical ones (not worrying about textures or looks) would actually be MORE efficient. I've actually disabled a lot of the different skinned-ones and increased the number of spawn rates on horde nights and got better performance, anyway. *shrug* I, personally, would just rather see 100+ zombies coming at me than a dozen "zombie this name and zombie that name" coming at me, with the occasional "boss" or the like. Feral wrights, for example, are badass lol.