Much less grip, but it's not excessive. The main thing you notice is floating at higher speeds since you're skipping over the loose gravel. A little wheelspin clears that right up. I wouldn't worry about it; be aware of the tires but otherwise drive normally. FWIW I run starspecs and am comfortable getting sideways with them on gravel.
The soft compound is actually good for the surface once you get down past the loose stuff. Even gravel rally tires are made from race rubber.
EDIT: I completely disagree with oldskoolWRX. Summer tires can even be the right choice for rallycross sometimes, depending on the surface. Also, euro rallycross is typically done on tarmac tires as the loss on the dirt is not nearly as big as the gain on tarmac.
EDIT again: obviously they won't work in the cold or in snow. I don't think that was the question, though.