It's not the number of Avatars...
Several factors contribute to the bandwidth issue with the Avatars.
1. The number of total Avatars available to display.
2. The number of members that can display Avatars.
For instance - say you have a thread with 20 posts. And each post is a different member with a different Avatar, that is 20 distinct downloads to display the thread - and a good thump on the bandwidth slice.
Each Avatar is pretty small (about 5k)...but add it up, if you multiply 5k times the number of posts in each thread, times the number of views for each thread - it adds up VERY QUICKLY.
So - it would speed up the forum in general and speed up the display time for each page (especially for dial up connections).
Another option is to have the Avatars hosted by the individual - like when you post a picture - the only problem with that is that it's very difficult to restrict the size of the Avatars...and that could get ugly really quick!
So - Master Woodie's watching stats pretty close and it will be determined pretty soon...