Regarding range, my derailleur touring bikes have a range of 630 percent. (High is 52/11, low is 24/32.) My lowest gears are of course only used on the steepest uphills, my highest two gears are only used for long shallow down hills or when I have a strong tailwind on the flats. Thus, the upper and lower extremes are rarely used, but are really nice to have.
For around town my Rohloff bike is fitted with a 44 chainring and 16 tooth sprocket. But for a trip where I knew there would be steep hills I used a chainring with 36 teeth. On that trip, I actually had both the 36 and 44 chainrings fitted to the double crankset. After the killer uphills hills were all completed, I added a few links and adjusted the eccentric to switch from the 36 to 44 to give me the gearing I wanted for the rest of the trip, which included gearing for some long shallow downhills.
I too would like a larger range than the 526 percent offered by the Rohoff. I however would not want the gear steps to be increased above the current 13.4 to 13.9 percent between each gear as the means to do that. Instead I think the ideal solution would be adding two gears for a total of 16. With this, I would not need a second chainring to give me the wide range I desire.
If you are wondering why I chose a 36 chainring for my lowest gearing, I rode up a really steep hill and noted the speed that I felt was the minimum speed where I could easily maintain balance and remain upright. I then back calculated what chainring I would need to give me that speed with a cadence of 72.
Quite frankly, I would not be able to pedal up a hill at my lowest maintainable speed if the grade was 20 percent. Thus, I do not need any gears that low.
