Is there a relatively simple formula for figuring this out?
Example: With 26" wheels, bike is set up with 19t in rear and 32t in front.
In order to get the same relative difficulty of pedaling feel, what's the gearing on a bike w/700c wheels? And is there a formula that allows one to figure this out for any gearing?
you could use Sheldon Brown's gear calculator here: http://sheldonbrown.com/gears/
Working theory in mountain bike singlespeedia is generally add two teeth in back when going from 26 to 29", which this sort of is, but you'll likely be using smaller tires on the 700c, so maybe only one tooth? \
Anyway, use the calculator.