Going from 22lbs to a sub 20 bike will not make much of a difference for you. If you want some more speed out of your cross bike toss the knobs and change the tires to 700 x 23's. Asides from the road bike being lighter and in a more aggressive riding possition, the gearing and crank size has a lot to do with it.
Still, it's much cheaper for the rider to loose a pound than it is for the bicycle to do the same. Spit a few times before you jump on, that's good for a couple grams.