City biking: Yeah, if mostly on the flats and mild hills, in traffic biking and not covering long stretches of ground rurally, 30-70/75ish gear inches should be enough, especially if the bike is "empty". My (non-frequent) folder is fully racked and panniered with trunk bag full of tools and for shopping (and hopefully touring as some point) so 55 lbs all the time (with panniers empty except for backup warm clothes), and my city has San-Francisco-steep hills, and I really need that 21" low, and even then, on the most steeps (like 15-20% grade), need to stand on the pedals or walk it up. Out of the city, I do use the 85" high, but usually only if the wind is at my back or on a mild downgrade.