GGs are currently marketed (and supported) as being able to download or stream, and that's consistent with my recent experience. The hardware was designed to do both, even though the software may have been rolled-out in phases.
When I used the GG2, I had no issues streaming content to my iPhone while out of home, as long as I had a "steady" 700kbps (or better) wifi connection. I never used a Slingbox, so I don't know if it streams any better with a "spotty" internet connection.
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