Wowsers, a 20 granny. I swapped out the crank on on my 26" tourer for a 42/32/22 and find that low.
Through working on two bikes with similar rear gearing (13/28) I've both swapped cassettes to 7 speed 11/34 and from 7 speed to an 8 speed 11/40 by changing the hub body.
I also agree with low gearing, even if it's just an odd bailout like the shimano megarange cassettes offer. Long time ago in my youth I stubbornly mashed my way up a big hill on a loaded 2x5 bike trying to keep up with a guy who had a 3x7 in granny gear and wound up hurting my knee which took about 6 months to fully heal. These days, if I'm worried about speed, I probably am not heavily loaded also.
