Generally, the lower bitrate you stream at, the more listeners you will get and the fewer problems they will have. Personally, I stream at 56K because I have a Live365 relay and they only allow bitrates up to 56. Plus, streaming at 56K keeps my cable provider from getting too steamed at me
As for broadcasting above 56K, Stephen, you have to have professional codecs. The free ones in Netshow Tools only go up to 56K.