I wouldn't call them race seats and they are quite heavy. However they are reasonably comfortable and do a good job of holding you in! Someone more qualified might be able to inform us of how 'strong' they are. Remember you might have to purchase rails also if you haven't got them.
i've had a ride in a couple of cars with them in. my only gripe is that the wings arent wide enough to accomodate my shoulders.... so i dont sit in the seat back properly....
not sure if they make another size seat, but definitly a try before you buy thing..