Just play "Example Short 23.976" and see what the PS3's info overlay says at the Super HD bit rates. For me, it says "High/SD" for both 4300- and 5800 Kbps. See an example in a post earlier in this thread.
My Sony BDP-S390 has the same stream info display and it reads "Medium/HD" for 2350- and 3000 Kbps, "High HD" for 3850- and 4300 Kbps and "X-High/HD" for 5800 Kbps. I think that it's just displaying according to the original bit rate ranges: >= 2350 Kbps < 3600 Kbps is "Medium/HD"; >= 3600 Kbps < 4800 Kbps is "High/HD" and >= 4800 Kbps is "X-High/HD".
That post was one of the sources that lead me to believe that it is a bug. That and the fact that the stream I was getting could in no way be actually SD.
Also, I managed to reach a US server through unblock-us today which did not provide Super HD streams.
Edited by tizmon - 2/10/13 at 3:08am