I've never raced on anything but aluminum. The possible advantages of carbon are weight and stiffness. As Erik said, the weight difference between carbon and a well-made aluminum frame (which I'd say the aluminum Crux has) is pretty minimal.
Stiffness is very dependent on frame design. There are things you can do with carbon that you can't do with aluminum, but if the designer hasn't done those things the benefit is just baked in. You can only judge that by riding both models hard. Even then, I think you'd have to be more sensitive to that sort of thing than I am to feel it.
One of the biggest benefits of carbon on the road is that it absorbs road buzz. My experience with that, however, is that the kind of vibrations that carbon smooths out are of the sort that you get from riding on chip seal. Bigger bumps like rocks and roots are going to transfer pretty directly regardless of frame material and only the air in your tires will help. Consequently, I'd say this particular carbon benefit doesn't apply to cyclocross bikes.