Shock valving

Uhhh.......no.

To start, please keep in mind that any perceived ride quality is subjective. Hence why I keep mentioning "tunable" (in addition to serviceable). What is comfortable and complacent for driver1 can be very different than the requirements for driver2. Second, I'll refer to "counter damping" below, which essentially means the force provided by the shock to counter the forces inflicted by the terrain. Mathematically speaking, this is modeled as a force F= -cv. Where F is force, c is the damping coefficient, and v is velocity. Cliff notes, the damping force is velocity (shaft velocity) dependent that acts against the direction of the shaft movement.

A digressive shock means the counter force produced by the damping of a shock decreases as the speed of the shaft increases. Specific to ICON, they use a two piece dished piston that preloads the valve shims (compared to a flat piston with shims that are not preloaded and lay flat directly against the piston). From the perspective of the passengers in the vehicle, the vehicle will feel stiff over slow shaft speeds because the velocity of the shaft is not fast enough to overcome the preload of the valve shims. With typical street and track vehicles, this is predominately preferred because it doesn't feel like the vehicle rolls as fast in corners (again keep the whole "subjective" topic I started with). Now change terrain to offroad where you hit washboard, whoops, or uneven terrain in general, the shaft speed (not vehicle speed) increases to compensate for terrain. The shock overcomes the valving preload and perceived ride quality improves. However...as you overcome the valving preload, you also loose counter damping force at higher shaft speeds. Meaning if you have a big hit (large whoop, rock, consecutive uneven whoops, etc.) because you already overcame the valving preload, there's nothing left to slow down the shaft speed and inherently you bottom out the shock because you just blew through all the valving.

Progressive (sometimes referred to as linear) on the other hand, the relationship between counter force and shaft speed is progressively linear. Slow shaft speeds don't have the same perceived ride quality where you can feel every pebble and cigarette butt you drive over. It gives that "Cadillac" ride quality as there is no preload on the valve shims and the oil bends past the valving predictably and consistently. Now again, change terrain to the higher shaft speeds, the valving characteristics don't change. The shims bend at the same rate as there's no preload to overcome. The shock will progressively increase counter force as the shaft speed increases. Hit some bigger terrain and the counter force increases instead of decreases.

TL;DR

Digressive: hitting stuff slower= more force, hitting stuff faster= less force
Progressive: hitting stuff slower=less force, hitting stuff faster=more force

All that said, as many know, I'm a bit of snob. I have very high expectations of my shocks and don't like making compromises. I start with a base valving and tune to my preferences, my rig, and my driving style. Anyone can buy a shock off the shelf and run it. Most people makes concessions because they paid money for something, so they will defend their purchase. I'm a bit different. If I don't like something, I have no problem stating it was a shit purchase and move on to something else, or tune it until I'm satisfied. I could not tune my ICONs to my subjective preferences and be even close to satisfied. I like predictability, a soft ride around town, and balls to the walls damping in the dirt.

 

I edited the "even close" bit almost right after I posted it.
I completely disagree with what the "superior handling" on slow speed digressive though.

 

Gotcha.
I'm a big fan of digressive for on-road vehicles that have limited travel. I always ran digressive in my track cars, but you are talking like 3" of suspension travel. Some find it helpful with our trucks on-road as well particularly with no sway bar (for the reason you pointed out). But when it comes to dirt, I like my shocks being soft over wash but be able to take a bigger hits when the terrain gets rougher, not the other way around.

 

Well our trucks come with coilovers stock. It’s a verbiage faux pas. But I’m assuming you mean tunable and height adjustable coilovers.
I’m no help here. I only buy rebuildable and revalvable shocks. King and ADS are my personal preference.