With comparable undercarriage (ie: Aero 3000 skis, Baumann floats, EDO floats, 26 inch Goodyear tires) a good ballpark is that the Husky will be 20 mph faster than the Cub. That's using about 55 % power on the Husky and over 70% power on the Cub, though. Realistically, though that's the way we run those two engines. At those power settings, the Husky will be burning about 7.5 to 7.7 gallons per hour, the Cub will burn anywhere from 8 to 9 gph, with a lot of variability in individual aircraft. That is assuming a Cub with a Borer (most of ours are 82-42) prop, and the Husky with the stock Hartzell prop.
Matt uses significant oversquare power settings, which yield a tad more speed, and lower fuel burn, but afford uncomfortable vibrations in my airplane. In any case, that's one of the beauties of using a constant speed prop.
There is simply no comparison in these two aircraft when it comes to cruise performance and economy.
There are, of course, other parameters to consider.
MTV