Originally Posted by
Rowan
I honestly don"r see the need for alternative cassette anyway. I think it should already have a 28T cog, and the 12T on the 28-12 won't give the same top speed as the 11 which the OP is alluding to. The Trek 920 the OP has should be quite capable of being ridden with the seven gears between 28 and 11 on the standard cassette.
It's marginally off topic but you make a good point:
Back in the days when "10-speed" meant 2 on the front and 5 on the back, we had to squeeze out every possible gear combination. We still an occasionally digit head going on about the wonders of half step gearing. Today, with 10 cogs on the back alone, we have such a plethora of stock gear combinations that I have a hard time understanding the need for customization.