I'm a Campy girl, but this is what I did.

Last year before a tour in Colorado, I put a 13/29 rear cassette to go with my double crank. It worked out great for climbing, and I didn't notice the lose of the very top gear (53/12 versus 53/13).
I switched out the double for a compact this year. For this year's Colorado trip, I also brought that 13/29. Although this was a strictly recreational ride, I definitely felt the lose of the high end, and I spun out more times than I would care for. If I was racing, I would have been limited. For a recreational ride, it was more important for me to be able to climb.