Only the Slingbox Pro HD model has the ability to stream Full D1 HD in or out of network. however in order to stream in HD quality remotely, you MUST have at least a 3.5mb upload speed from your ISP. anything less will cause the image to be downscaled to the available bandwidth.
All other models such as the solo or slingbox pro stream at a max rate of 640x480. What may be confusing you is those models although they give the ability to connect an HD enabeled peiece of equipment via component video cable sets, they are not capable of streaming in HD neither in or remotely out of network.