What I mean is that depending on the stream rate (96, 128, 192, etc.) that you use, depending on your up and down speeds with your ISP, you may be streaming faster than your bandwidth can handle.
For "prime" stream speeds, honestly I've found anything below 128 just doesn't have a very good sound quality. You can get away with 96 but you'll notice a huge difference in the sound quality of your stream.
Stream providers are stream providers in my opinion. I pay 500/month for 192/kbps and 200 listeners (not giving specifics just an example) and never have an issue with stream uptime or quality. I would suggest asking around in world of other DJs and find out what they're using.
If SL is being extremely laggy it will also cause you to have issues with your stream as well. I would also suggest clearing your cache about once a month or so if you don't already do so. I hope that helps you out!