Sounds like you are on a real low BW shared server. 125 users in this business is a joke, try a few thousand as the norm for a decent day.
Lots of things can determine what your server can handle, but one of the main things is how big of a pipe is connecting your server to the internet. How much memory is also important and how fast the processor is. If you are on shared hosting then how many people are on your server and how much traffic they are getting will effect you as well.
Maybe it is time to get better hosting, check out the drop down menu in my tag and select M3 Server.
