My Twenty came with a 15 tooth sprocket on the hub, which I changed to an 18, which is very easily done. That made a big improvement. But I don't do any hills on it, and still hardly ever use the top gear.
I'll think about whether changing off the sprocket will give me a low enough gear. That may be something to look at even if I also change the hub. Atlanta's piedmont, so most areas I ride are hilly.