Effective travel depends on A) how and where you mount the shocks and B) What you define wheel travel as...
A single wheel can more more up and down in articulation, than the complete axle can move up and down. This depends a lot of the width of the axle/tire/wheel combo
Axle travel (both wheels moving up/down the same amount, like in a jump), for a vertically mounted shock would be: Inches of shock travel * (distance from LCA frame pivot to axle centerline / distance from LCA frame pivot to lower shock mount).
The shock spring rates and damping ratios will be reduced by the same factor that shock travel is increase by, if the above ratio is not 1:1