I've got a '78 City Bike that I've been rebuilding for a few months finally got it running like a dream. Top end is at about 25 or so which seems consistent with specs. I'm wondering though if there is a more efficient sprocket ratio than the stock setup. 42t rear and 9t front. I'm mainly looking for a little more torque b/c the acceleration is not great but a little more top end wouldn't hurt either. Anybody have any recommendations?