If you're streaming outside of your local network and aren't using an old version of the SlingPlayer software you're using the man in the middle system that Sling has. The receiver uploads to the stream to Sling, sling sends it to you. When you're streaming in this fashion it's limited to SD. It won't send an HD stream to the sling servers.
If you use an older version of the SlingPlayer software you can stream as much bandwidth you want, up to what your network will support. Of course this requires that you have access to port 5101 on the 922 from remotely. However, the older SlingPlayer software won't support HD with the 922. So you're still limited to SD.
So I really don't think you can stream HD outside of the local network. You can get really good and high quality SD. But not the HD resolution.
To answer your specific question. I'd agree with the 500k suggestion as an absolute minimum. Anything above that can just let you get smoother and better quality. Around 1Mbps should give you a pretty consistent quality SD stream and anything above that is just gravy. To a certain extent what you need will also depend upon what you're watching. If you're watching sports, you're going to want more than say a drama or comedy series. The more often the entire picture changes the more bandwidth it's going to want.
P.S. I strongly suggest AGAINST leaving 5101 open to outside your network with the 922 right now. The password to get into the 922 is admin. The SlingPlayer software will let you change it and the new password will work but the 922 will continue to accept admin. On the next reboot of the 922 the new password will be gone and it'll be back to only accepting admin. So at this point if you're allowing remote access to the 922 other than through Dish's website, you're allowing EVERYONE in the world in.
