night cycler, The Ultegra line-up includes two additional cassette options:
11-23: 11-12-13-14-15-16-17-18-19-21-23
11-25: 11-12-13-14-15-16-17-19-21-23-25
11-28: 11-12-13-14-15-17-19-21-23-25-28
11-32: 11-12-13-14-16-18-20-22-25-28-32
12-25: 12-13-14-15-16-17-18-19-21-23-25

You can see how as the range decreases the more close the ratio between each cog becomes. Which cassette to choose depends on terrain and crank set chain ring option (standard or compact).

Brad