When I bought my bike it came with an 11-23 tooth cassette and a standard compact crank (50-34 tooth chainrings).? I quickly found that was a lot higher gearing than I was strong enough or fit enough to utilize.? In my second year of riding I upgraded to an 11-25 cassette, which helped a bit but still left me wanting more without going to the expense of a triple crank (and Lynn told me only gapers ride road triples, but then I pointed at Doug's Litespeed road triple).
I have also been watching SRAM's efforts at using 2x10 groups to compete with market segments that normally used triples.? The advantage of the double crank over the triple is weight, less gear overlap, and simplicity/reliability.? SRAM introduced their high-end XX a while back, and this year introduced their APEX group for road bikes - and the distinguishing feature of the APEX group was 11-32 and 11-36 cassettes (and maybe smaller chainrings).? They also introduced an 11-32 cassette for their intermediate level road sets.
I ordered a SRAM PG1070 11-32 cassette last week and installed it earlier this week.? The lowest four gears are now 32, 28, 25, 22 which give me two gears that are lower than the 25, and based on a couple of rides it works well.? Shifting is as crisp as the Ultegra cassette, and I can now go up some of my standard hills at the same speed but with a faster and less leg wearying cadence.? I'm very pleased and thought I would pass along the info in case others wanted to try.? But there are some things you need to know.
Chainwrap- My Ultegra RD6700SS short cage derailleur was designed for a max 28 toothi cassette and can't carry enough chain to support my full range of gears.? Its rated at 33 tooth chainwrap, which is "cassette gear diff + crank gear diff" or (28-11)+(50-34)=33 teeth.? My new cassette is (32-11)+(50-34)=37.? What does this mean?? I can't use the 32 tooth cassette gear when I'm using the 50 tooth front sprocket. A good rider wouldn't crosschain that way anyway, so that's not a big restriction and well worth getting the bigger gear. There is also an Ultegra RD6700GS medium cage derailleur that has a 39 tooth chainwrap capacity, and I may decide to get that with a SRAM 11-36 cassette.
I didn't need to replace my chain, but depending on what gear you had it might be necessary. Most shops remove some links of chain when they install a new chain (especially if you have a compact crank).