Yeah I had big dreams of getting horses on the nether roof but now it's impossible.

Guess again!

(haven't tried this in current versions, but I see no reason why it wouldn't work)

Oops, had no idea this was an issue and I may have already slightly done it.
Admins etc. msg me in game if you want me to show you where so you can repair it.

If you want to check the actual tick rate use some in game measure of time and time how long it takes irl.
Some examples: serverplz ticks at a timed interval
hopper timers
dropped item despawn timer (which should be 5 minutes)

Generally the server seems to run at about 15tps with about 30-40 people on although it has obviously been much lower at times.

Also you will need to be within 3 chunks for them to grow with the current 4 chunk render distance.

Nysic, you're the best!
Also, massive thanks to Cellexya for adding me!

I know from my guardian farm over a year ago back in 1.8, the guardians seemed to work like a physical spawner. I could let the guardians build up no matter what and it would consume the mob cap very quickly. It took it nearly 30 minutes to get started though

Yeah, the guardian spawns will be a bit different because the number of spawnable blocks are so much higher. Since they just need a water block the area around a monument has over 70,000 blocks they can spawn in if they're all water. The game only checks the mob caps at the beginning of each spawning cycle, so the cap can be massively exceeded if there's lots of spawnable blocks around. This happens noticeably with guardians and squid, I had over 200 guardians spawn in a couple of ticks the other day!
Obviously the same is true for any other mob if you make the spawn area big enough - it's just a ton of work.

Since I'm over a fortress, I was hoping for wither skeletons to spawn as well, but not sure that is how they work. I haven't read up on the mechanics regarding how they spawn yet and what conditions have to be met. It may be as simple as building the spawn pads out of nether brick in the fortress chunks, I dunno.

Sadly they don't work like that.
Check out these videos for more info (they're both the same, but 1 says 1.9 in the title so you know it's legit):
https://www.youtube.com/watch?v=RcQzqk_8OTo
https://www.youtube.com/watch?v=PJLJ5fynNGw

I noticed this too about the lazy chunk distance. Skeletons and zombies will be rendered but not moving and won't burn in the light til you are within range of them to move,

A fun (and possibly useful) way to show this is to put a block of sand on a regular piston and attach it to a clock. Walk away while the clock is running. When you're far enough away that the sand is in a lazy chunk instead of appearing to fall when the piston depowers the sand will teleport 1 block down. If you use red sand it will magically turn into normal sand :)

@pand1024 If you want a good test to see if your idea will work. Open a single player world set the the render distance to 4. Quickly mockup the most basic version using /fill and /clone. If it works theres a good chance it will work on the server.

This is great way to test if there is any problems with the grinder!

TL;DR

You're right, the bigger the spawning area the more spawns you'll get. The problem with the idea of 'stealing' mob spawns from other players is that you'll be killing all your pigmen very quickly, but other players probably won't be killing hostile mobs around them as fast. I think this means your farm will slow down over time (not 100% sure about this).

Regarding the server render distance and redstone/mobs: Redstone contraptions keep running as long as they are within the loaded chunks.
However in minecraft there are two different types of loaded chunks; fully loaded and lazy chunks. Fully loaded chunks process everything, lazy chunks don't process entites. For CM as far as I can tell the first three chunks out from the player (including the one you're in) seem to be fully loaded, and the forth is lazy. You probably don't want the farm running into lazy chunks to avoid the need for chunk loading.

The iron golems should still attack the pigmen when you're further than 32 blocks away as long as they're not in lazy chunks (might want to test this - I'm not sure).

Also in case you're not aware I think there's an issue with the iron golem pigman farm. Pigmen can occasionally summon regular zombies as reinforcements, which will attack the golems. The golems will slowly die - this does take a while though.

I'm going to make an attempt to clarify on some points here, in the hope that anyone else asking these questions will find this useful.

Mob Caps
All mobs are spawned up to a certain cap. In a single player unmodified game the hostile mob cap is 70. On multilayer servers the mob cap is dependant on the number of chunks loaded according to the formula:

cap = chunks / 289 * 70

The mob cap is shared between all players.
On CM chunks are loaded around the player with a radius of apparently 5 (although I suspect this may have been changed recently to 3 or 4), giving 100 loaded chunks total. As an example; with 20 players online the hostile mob cap would be approx. 484.

Interestingly this also means that if 1 player has 484 hostile mobs around them, no mobs will spawn for other players unless one despawns!

Hostile mob spawning

Each tick the game checks if the mob is met, if not it will attempt to spawn up to the mob cap. The game will randomly check for spawnable blocks (i.e. opaque, low light etc.) and spawn mobs on these as they're found. Notably on severs these spawns could happen for any player.
One consequence of this is that players with more spawnable blocks around them will be more likely to have more hostile mobs spawn around them. This considerably reduces the spawn rates at spawners since spawners generally have relatively few spawnable blocks compared with a random spot on the ground at night.

Mobs spawns aren't just capped the rate decreases dramatically even if you are half way to the cap.

I'm not sure where you got this from but I don't think that this is true, and I cannot see a reason for it.

Mob farms at the build height and vertical distance

Hostile mobs will instantly despawn if there is no player within 128 blocks. However it's important to note that they can still spawn over 128 blocks away. For the horizontal axes this is irrelevant on CM since mobs beyond 80 blocks from a player are unloaded. Vertically however it will still occur.
As pand1024 said chunks go from y=0 to y=258. This is why mob spawners work best when built at the hight limit. Building over an ocean and lighting up caves below etc. will increase spawn rates, but not by very much since any mobs spawned there will instantly despawn if the player is up at the build height.

Hopefully this all makes some sort of sense and is even remotely useful to anybody
XD

Well... here is a screenshot of it after my visit

Baron being the mischievous little imp that he is used lots of TNT to decorate his abode, and several trapped chests. So after literally jumping off my chair I was blown to kingdom come along with the room and everything in it.

Oh, and the diamond armour was actually leather.

GG Baron, GG
XD

Wooo! First ever forum post!
Also a found Barons wondrous abode and now I'm rich beyond my wildest dreams. Diamond armour up to my eyeballs.

Everyone else was too slow, you all lost out bigtime! I got all the loot!!