I only know S13 spring rates, but I think that the Flex is the only coilover available (from the factory) with 5/4 rates. Of course, you can always buy different springs for Tein coilovers for approximately $100 a pair.

To stay on topic, though, I haven't heard anything about SPL parts coilovers. Not to knock them, but there are plenty of Japanese coilovers that have been tested in the field for years.