Look at the other part of the data posted by hermes. There is a big difference in the percent change in shifting gears in a double vs a triple. Unfortunately bikes are getting more and more marketed to just the young and what's easy at 30 or 40 may be next to impossible after 60.

I don't care what drive system is used, I still can't find a sweet system:
Criteria:
1-- low GI at least 24, ideal 22
2-- high GI at least 130
3-- steps between gear shifts never greater than 9%
4-- minimum double shifting

Best i have found is: 28-42-53 with 11-27.