I think I lucked out. I started sizing the current stock alloy crank set on the frame (that is frozen onto the bb) and found that I have two good stiff ratios with perfect chain tension. 34 x 17 and 42 x 18 (?). I'm not positive on the second one because I haven't counted the teeth on the sprocket. But this means I can have a 18t freewheel on one side for cruising in rain, and when it gets nasty, snowy, and icy I can do the 34 x 17t fixed and have perfect control and traction at a slower pace.