We'll tell you straight up that while we appreciate the appeal of Dura-Ace cassettes, we understand why you would choose Ultegra for your bike. Smart racers routinely save money by going with Ultegra cassettes; the money saved can go for other weight shaving measures.
On the plus side, Shimano Ultegra CS-6700 Cassettes are lighter than their 6600 brothers, doing a nice job of closing the gap on Dura-Ace. The tallest cogs are riveted onto an aluminum carrier for weight savings, and they're more gentle on aluminum cassette bodies. Shimano has improved their manufacturing quality; now they can make the ramps stronger because they can build to tighter tolerances. And the ramps themselves have been revised for faster shifting.
The Ultegra CS-6700 Cassette has ten cogs and comes in the following ratios: 11-23, 11-25, 11-28, 12-23, 12-25. It comes with a nice alloy lock ring. The finish is Chrome (a color, not old-style chrome-plating).
The 11-23 includes: 11,12,13,14,15,16,17,19,21,23
The 11-25 includes: 11,12,13,14,15,17,19,21,23,25
The 11-28 includes: 11,12,13,14,15,17,19,21,24,28
The 12-23 includes: 12,13,14,15,16,17,18,19,21,23
The 12-25 includes: 12,13,14,15,16,17,19,21,23,25