The Shimano Ultegra 6700 cassette has remained unchanged for the most part. However, a few minor improvements over the 6600 version will make a big impact on your shifting performance. First, the tolerance between the cogs has been refined and made more robust so you'll get into gear quicker and more accurately. The 27 tooth sprocket has been dropped in favor of a 28, and the aluminum carrier has been machined down to lighten it's weight. The overall look is such that the Ultegra cassettes are almost indistinguishable from their Dura Ace big brothers. As you would expect, it's another step forward for the increasingly advanced Ultegra group.