I'm watching my Slingbox HD right now on my HTC 8525 over AT&T's 3g network. I'm getting a brisk 1956kbps connection over the 3g and its working just fine
You can't get 1956kbps in the Sling app, it's limited to 512kbps or something.
Not if you edit the settings file. It's really not that hard. Google it. But you are correct. Without editing it does cap at 512kbps, I forgot that I modified mine ages ago. (like over two years)