How many players would this...

[Drocona]

I can host a 20 player server filled with bots on my P3 933MHz without lag.

although, it's a fact, EdwardTobia, that you can not host 14 players on a 512kbps connection. That means you have to set maxrate to 4500 or something near that amount, which will result in high choke building up from the 6 player mark, before you get to 12 players the choke will get the tickrate below 20, thus resulting in lag.
Even if you manage to hold teh tickrate above 20 the quality will be that low.