Guys - I would not recommend going to a lighter spring to reduce the height. This will greatly increase "sag" and will affect the handling. (Think of a car with worn rear shocks that is riding ride soft and low.)
Shortening the travel of both the front and rear suspension is the safer and better solution. This is done by limiting the travel of the suspension. You want your bike to be balanced with the spring rates set for your body weight. By shortening the travel (requires modification of the shock), you achieve lower height, with less suspension travel... but with good, useable and balanced suspension.
I recommend that you speak to a suspension specialist before spending money on softer spring.
Hope this helps.
'05 KTM 950; '11 KTM 350 XCF; '08 KTM 250 XCF-W; '05 Montesa 250 4RT Trials