Originally Posted by TrojanHorse

I am down to a regular compact now (50/34) and 3 different cassettes depending....

11-26 for general duty / flattish riding or short hills (< 10 min)
11-28 will tackle just about anything, including 1+ hour hills
11-32 really will tackle anything - I put this one on for special rides, like trying the mt Baldy ski lifts or the Palm Springs tramway. If my garmin says 15% this is the cassette I want on.

The trick for long rides like a century is that it is always nice to have an easier gear than you might normally have because you just get tired after a while. Go find yourself a 12-28 cassette, they're cheap enough and you will probably appreciate that 28 cog at some point during your ride. 3 teeth isn't a lot until it's the difference between your heart rate blowing up and you keeping pedaling.