I am bit confused by your post. I will try to bring a bit of clarification for you in this. Normally the download speed is higher than the the download. I actually never seen normal Internet provider with more upload speed than download speed. There is a exception called SHDSL were the upload and download are excatly the same. I don't know where you are located but normally providers never have more upload than download rates.
What you need for watchig HD:
In the location where your Slingbox Pro HD is:
1. You need a good upload speed, as the Sling Box has to upload your content to the Internet (somewhere to you ;-). In case other people are using the Internet in this place in the moment you need a even higher speed as the users there are using as well some bandwith (depending on what they are doing). I would recommend 4 Mbps. As minimum I would say 2 Mbps. I our days you should not have a problem to get 2 or more upload speed depending on where you live.
2. The download does here not really matter.
In the location you want to watch:
1. You do not need a lot of upload speed as you do not wana sent something.
2. You need the best download speed. Minimum 2 but better 4. Normally depending on where you live even 20, 60 or even over 120 are possible. Here as well if others are using this network as well you need alot more.
To really check wich speeds you have you could run a Speedtest like: http://speedtest.net/
Try to select the location that is close by your localtion it will indicate up and download speed seperatly.
You have to run it once in the same place like the Sling Box and read the upload speed you can ignore the download. And a second time in the place you want to watch, there you look just for download and can ignore the download.
Check the Internet for providers in your country speeds like you mentiond in your post seem a bit out of date for me. There must be plenty of providers arround you offering more than this.
Best of luck. Hope this helps.