Just downloaded the spec sheet for the Shimano Ultegra CS-6700 cassettes. Don't remember seeing it before, but this sheet shows a 12-30T cluster. Cogs are 12-13-14-15-17-19-21-24-27-30. Is this something new? None of the normal on-line vendors show it as being available. Might be nice to have if the current rear derailleurs will handle it, which the spec sheet seems to imply. (p.s. I see that Tiagra has a 12-30T, but Ultegra would be nice.)
Dura-Ace is now available in 11-28T, but at almost three times the cost, I run with Ultegra clusters.
Tech doc here: EV-CS-6700-2924B