No, you can get different spring rates with either kit. The difference is that the Flex have adjustible shock bodies allowing you to lower the car without losing suspension travel and even gaining travel over OEM. If I remembered correctly, that is where the $400 difference comes from...well worth it IMHO if ya want to lower the car any reasonable amount.
90 MX5 281k miles! - euro spec, Porsche Riviera Blue w/black hardtop, 97 motor swap, vintage Borbet rims, GC, FM shock hats/frame rails/rear sub-brace, AGX, sway bar, stb, Fidanza/ACT combo, EBC Yellows
92 COMMA SM - new paint coming soon...