I don't thing a double chain ring is an option, since we're talking mostly rolling hills, short stretches of steep climb followed by downhills or flats. I'd hate to have to get off the bike to switch chain rings on top of every hill.

Fietsbob, how did you get the third sprocket on the bike? Googling wasn't very effective. Are there instructions somewhere online?

How hard was it to obtain and install the Mountain Drive?