I typically get 8000 kbps (as you do) when watching my SB from a computer within the same local area network as the SB. In this case, the streaming signal is only being transferred through my router, and not through my modem or the Internet at large. But when watching my SB from any location OUTSIDE of my LAN -- even if it just a test connection from my neighbor's computer network, I never achieve speeds higher than 3,000 kbps, and more typically the speeds are between 1,000 and 2,000 kbps. Theoretically, my DOCSIS 2.0 cable modem should be able to deliver much faster speeds than this, and visits to bandwidth testing sites such as www.bandwidthplace.com indicate that my upload speeds should be up to 4000 kbps. But I simply do not achieve this fast of a speed for video streaming.
You might look at "bandwidth speed optimization" websites such as www.speedguide.net for tips on how you might be able to increase the speeds for your viewing computer, but I generally find that it is the UPLOAD speed of the network where my SB is physically located (and not the DOWNLOAD speed of my viewing computer) that is the controlling factor on the speed of my streaming. And the total upload speed from SB to viewing computer may also be influenced by all of the intermediate points in Internet Land that the data pass through -- and over which you may not have any control.