Super HD is not a higher resolution, just a higher bit rate 1080p video encode. The regular "1080p HD" is 3850 Kbps and "1080p Super HD" is either 4300 Kbps or 5800 Kbps. The extra bits should provide a sharper picture (5800 Kbps is half again as high as 3850 Kbps), though we have no objective proof that it actually does.
Some of us have been getting Super HD with ISPs who aren't signed up to access Open Connect using a method discussed in the Super HD thread starting with this post. There are caveats--you should read through to the end of the thread to hear some of the problems we've seen and the workarounds we've found.