I took a look at the Koni FSD's and they seem to be the ticket. FSD stands for Frequency Selective Dampening. The way they operate is through a valve that controls the flow of oil through the shock chambers thereby adjusting the dampening based on the frequency of the oscillation. For example, if you are going through a washboard type of freeway ruts the frequency of the oscillation will be more than 10 KHz. At this point the valve is fully open and the shock will have very little dampening which will keep the vibration from going into the coach and will allow the energy to be absorbed by the springs or air bags. This is what you want to happen. You want the energy to be absorbed by your springs or air bags as opposed to your rear end. However, the problem with all of the energy being absorbed by the springs/air bags is that the suspension will feel "soft" and unresponsive when lane changing or in an emergency maneuver. Herein lies the beauty of the Koni FSD; they have a way to change from mushy to firm. For example lets say you are making a lane change, or say a semi passes by, the oscillation will be less than 10 KHz at which point the valve will close and provide full dampening and stiff resistance to movement. At this point the suspension is "tight" and will provide greater control than if the suspension were "soft". It makes a lot of sense to me, and they will be my next shock absorber. As for the Bilsteins, I don't know how if they can adjust from "tight" to "soft" in real time.
Koni's are probably the premier shock (and priced accordingly), but in my mind the fundamental question is whether the factory shocks are doing the job adequately or not. If the ride and handling are OK, why change brands from whatever the OEM equipment is/was? And if not, then the question becomes what is needed to give the desired result? Stiffer is not always better.
The suspension is designed to have shocks of some given stiffness and damping rate and changing that affects the whole system. Sometimes the factory errs in shock selection, but more likely they merely chose a different set of compromises than we might have chosen on our own. Some people like a firmer feel regardless of the effect on ride, while others want a plusher ride above all else. And of course, the type and quality or road surfaces you drive can, to some extent, make one type of shock more desirable than another.
And it's not so much a brand question, since Koni, Bilstein, Monroe, etc. all make shocks with different damping rates, which will yield different results without changing brands. Sometimes what you may want is simply a different model of shock (different part number) than the OEM version, i.e. different damping rate and different total damping effect. Since most of us don't know the engineering parameters anyway, the adjustable Koni's may have an advantage in that you can experiment to find what you prefer.
Thanks for the replies. At the moment I am leaning toward the Konis. We have this separator between Oregon and Arizona called California. I-40 and the southern half of I-5 really suck! I think you need some good shocks for that area.