Aight... well, thanks guys.
I suppose that different outfit/colors is better than nothing for sure. I hope TFP will consider adding more zombie types in the future, but after checking the forum a bit more, it seems like a frequently requested thing.
As for the main point of my post, I guess I'll be patient and wait for Bandits... still, even if we do get bandits -- if would be great to have sliders for that too! More zombies, less bandits, or vice-versa. Perhaps some people won't like them, so sliders for both could definitely help here.
Even if performance is the main debatable point for too many zombie spawns, I think the bottom line: it's our problem if our PCs can't run it (unless it's a server/engine limitation thing at a DEV level). Regardless, I'm not experiencing issues with the Duriel x16 mod -- even the x128 mod runs smoothly... so I dunno! Food for thought. They can just put a disclaimer on the slider that says "use at your own risk"...
Thanks for your responses and consideration nonetheless