Originally Posted by banerjek

Consider these cassettes:

12-25: 12, 13, 14, 15, 16, 17, 19, 21, 23, 25
12-27: 12, 13, 14, 15, 16, 17, 19, 21, 24, 27

Note that they are exactly the same except the last two cogs which you should only be using when you're in the small ring. Chances are that if you want the 25, you want the 27. So you suffer no penalty for getting a lower gear.

11-23: 11, 12, 13, 14, 15, 16, 17, 19, 21, 23
11-25: 11, 12, 13, 14, 15, 17, 19, 21, 23, 25
11-26: 11, 12, 13, 14, 15, 17, 19, 21, 23, 26

With the 11-25 and 11-26, you lose the 16 which is useful but you'll notice that the width really only comes at the bottom of the range which shouldn't get used that often.

11-28: 11, 12, 13, 14, 15, 17, 19, 22, 25, 28

If your rings allow you to use the mid and upper ranges of your cassette, everything is still one tooth apart. In the cassettes above, we see that riders that predominantly use their top 5 cogs won't notice any difference from the 11-23 and those that predominantly use the top 6 won't notice a difference from the 11-25. This is still definitely a hill cassette but wider spacing is not as much of an issue at the low end when you're grinding up a hill.

Of course, maximum selectivity would be with a triple and a corn cob. You'd have tight ratios anywhere you wanted them.