I have a 105 10 speed, 12-25 and have become addicted to it because the very close ratios keep me on the "boil". Looking at my cadence, I see that I tend to upshift very close to 100 rpm but my best power comes at around 94. It just so happens that an upshift with my setup drops my cadence by 6 rpm, perfect. While my main bike was being serviced last week I rode my backup bike, 11-27, 8 speed and the upshifts were too much, took me out of my powerband. The original rear cassette on my 2nd bike was 11-32, that really was too much, at least for me.