No, they are no longer than Sahara springs. What makes the Rubicon sit higher is the bigger tires they come with from the factory. Basically a 31" tire, compared to the 29" tires most other models come with.
Stiffer not longer. Rubicon and Sahara also share the heavier spring rates. There are several combinations specific to the Rubicon and Sahara that you wont find in the sport or x.