Interesting thread, and an issue that I think about from time to time. This is my second season, and I'm finding that hills are easier (a relative term!) than they were last year - so I'm definitely getting stronger and have dropped a few lbs. But, I have a double (53-39) w 12-25 cassette, and for the most part, I've avoided extreme climbs. My driveway (about 1/3-1/2 mile) is about a 10% grade, and I can make it up that, but I'm not sure that I could crank up that kind of grade for a more extended distance. (By the way, the town would not take this on as a public street because the gradient is too steep).

I've been thinking that a 12-27 cassette might be a reasonable compromise unless I get into more mountainous terrain, although I am managing well so far.