Well i have a live axle vs with the normal width spring insulators. I found that superlows all around was pretty average, the ass wasn't dropped to the height i'd like it what so ever! Took it back, they replaced with ultra lows in the rear, with a full tank of petrol, looks pretty good. It will still sit level no matter if the tank is full or empty. As for the scraping, i haven't had any issues with it for the mere fact i have 50' 17's on it...The normal height of the tyre's are 45' 17's...So they are a bigger tyre on the rims i have. With that smaller normal tyre, it is possible that you may scrape quite a fair bit over bumps.
Cheers, Boojakz.