For cadence, I'd go to:
http://sheldonbrown.com/gears/
and enter your gear ratios and tire setup. Actually, I'd use the mph (or kmh) at 90rpm (similar), per gear, and go by that. You could print it out, or just remember that x gear ought to be y mph--odds are, you won't have to remember the "proper" speed for the lowest and highest gears, just whatever ones you are using most often.