The upload matters. Remember you are watching what is being sent from your home receiver through your home Internet connection. If you don't have a fast enough upload connection then it doesn't matter hoe fast your download speed is where you are.
sounds about right ... note though ... that if you're doing it inside your home network (ie. pc in your back office not near the receiver, but in your same house network) you would be getting as fast as it can deliver it to you.
When connected to a Sling Adapter ... administrivia still goes up to Dish/Sling, and configurations, settings, controls, link quality assessments come back to the pc/device that's receiving the stream .... the video/audio data stream, in *most* cases, is direct between where you are, and where your Dish Receiver is. So if you're inside your house .. you still need the internet to work (authentication, and still does all the above /config/QoS/etc) but the link between you and the dish, if 100 meg could use that full 100 meg *if* it were able (max I've seen is 10~11meg)