David,
The Koni FSD shocks are not adjustable ... but they are sold by vehicle type ... so the factory is most likely using various valving parameters per vehicle weight. I had to wait a long time - and also bug Koni - before they finally introduced a Ford E450 version early last year.
The Koni adjustable shocks are a whole nuther animal - with probably about the same performance as my pickup truck's 10-point adjustable Rancho lifetime warranty shocks - in that both the adjustable Ranchos and adjustable Konis most likely have identical damping action in both directions (extension and compression). I know that the Koni FSD shocks are hydraulic - not gas. I don't know if the Koni adjustables and Rancho adjustables are hydraulic or gas. However, I think that I'm a fan of well made good old fashioned technology hydraulic shocks. As usual, it's probably more expensive to make high quality long lasting hydraulic shocks than it is to make long-enough-lasting-for-the-average-consumer gas shocks ... I'm just guessing on this issue, though.
The adjustable Koni shocks do have a BIG NEGATIVE though, as compared to my Rancho pickup truck adjustables. I think that one end of the Koni adjustables has to be disconnected to adjust them by twisting them. To adjust the Ranchos, I just crawl under the vehicle and turn a knob. I have done this many times on my pickup truck trying and trying to stop it's front-to-rear rocking .... all to no avail. What's up with those extended cab short bed Z71 one-half ton 4X4 GMC pickups .... anyway? I even have special rubber shackles on the back ends of each rear leaf spring to address this issue.
I installed the FSD Konis on the rear of our motorhome to address an issue that's especially - and mostly - a problem with putting a relatively low weight motorhome on a chassis built for much more weight. I wanted the advantages of an overkill chassis but without the rear leaf spring stiffness disadvantage. Short of removing a leaf in each rear spring - which is a poor option IMHO - I finally installed the Koni FSD variable damping shocks back there that on highway cracks and potholes act like no shocks. Spring stiffness on highway cracks and potholes is bad enough without adding shock stiffness to it.