They are reasonably firm, yes, and that's more or less why I'm selling them (ie. the roads around my suburb are equivalent to a minefield). If you can live with a slightly ride, though, you would really have to look very hard to find better enigneered and better handling items.
As far as fitting a sedan, I cannot see why not, but probably best to use the search function in the suspension forum. Can anyone shed any light on the subject?