I have no solid answer. Here's only what I've read.

Is it a cheat? Could be. I've read that a cheat can send extra packets your way, so that you are bogged down with more info to cram down your bandwidth.

If not a cheat, then what? I think the most plausible explanation is that naturally there is more packet info with more players, but it shouldn't be so bad as to cause the kind of issue you are stating. So there are so many factors to consider - your UT setup, your hardware, the traffic on the connection to the server, the server's hardware, and the setup of the server itself (this last one being the only thing I can control).

I know I've done the best I can to keep the server speedy. 99% of my mutators are extremely light processing DURING gameplay. There is one mutator left, CCProtector, that does lots of code in Tick(), I want to redo that to make that light too.

I will look at something else I could set, I will see if enforcing a max client rate on the server would help, I want to research that first though.

I know you do lots of reinstalls, the two things you should alway remember to reset are CacheSizeMegs, and your NetSpeed.

That's it for now.

I'll let you know after I've researched and experimented. I'm not even sure they are settings that would help the server, they may only be relevant to the client.