Timpo,
That illustration shows a pretty simple spring, and though many seats have springs built into them, that one is going to offer more travel.
A point that recently occurred to me though (I can be slow like that, so maybe everyone else has already considered this), is illustrated clearly in that pic. That's the point that most seats allow for a range of positions for the clamp to be fastened. My original thinking was that this "range" was to allow for different distances from the handlebars for rider positioning. What I just realized is that not only is that a factor, but you are also changing the leverage your weight has on the springs built into the rear of the seat!
The further forward the seat is positioned the more leverage your body weight has on those seat springs. The further back the seat is, the less leverage your body has on those springs.
Point here being, you might want to consider that when mounting your "cruiser" style seats (e.g Cloud 9). With the clamp mounted forward, I'm thinking it might be difficult to get full travel from thse springs even on bigger hits. With the clamp mounted towards the rear, the springs may bottom out frequently.
So, something that seemed so simple at first, suddenly becomes much more complicated! -Al