Although mine is lowered, you can use them with stock springs. I am very happy with them and for the price you cant beat em. Check Ebay for great deals on a complete set shipped.
I also cant answer that, but can simply say that I'm very pleased with them when combined with Eibachs. If anything, having more spring travel should allow them to perform better I'd think (E.g., the Eibachs dont give them a lot of room to compress, and they still work well).
Lowering the car will affect the shock travel, therefore the shock won't perform as well. Shocks are designed to work with stock spring height and not specifically designed for lowered vehicles, unless you go with tokico's coil over kits but those cost considerably more. However on a midly lowered car, I'd say up to 1.5 inch drop, the shock will perform adequately. I run them with my steeda springs and the ride is very tolerable.