The bumpstop typically adds spring rate which has to be dealt with in the rebound valving. It is a balance.I think a lot of it is subjective outsidebthe context of racing. With a nearly stock street legal passenger vehicle a digressive shock gives you tight handling on curvy highways and some relief on surprise bumps, but then it's a really good idea to have Timbrens or some other kind of improved bump stops to help soften the inevitable slam. Linear is better when you have a performance suspension.
It think King and Fox is more linear than anything. That is just the nature of most non-position sensitive shocks that are not being tuned to be 'firm' at slow speeds like the digressive pistons in Bilstein and some Icon stuff.So, I guess the Bilstein shocks are perfect for me. My travel is limited and they are what I can afford. Actually, that's the reason why I bought them instead of Icons.
I thought King and Fox are progressive?
To make them digressive you would need a dished piston like Bilstien uses to pre-load the shim pack. There is no extra pre-load to be had on Fox and Kings, the nut is tight. You can plug bleed holes for more slow speed damping.King and Fox 2.5 are nearly linear. You can add shim preload to make them more digressive
Stiff springs are the root of all evil generally, especially when talking about off road stuff. I find that you only want enough spring rate to hold the vehicle up to the proper position. Having some preload at full droop is good. Zero, of negative, spring rate at full droop is bad. Roll control should be mitigated with suspension geometry and weight location when possible. If you can't make the vehicle happy with that, add a sway bar vs adding stiffer ( usually digressive ) valving.If a vehicle has too stiff of springs, no amount of shock will solve the problem. Progressive shocks can be paired with progressive springs. They are useful for suspensions with somewhat limited travel (IFS for example) where a progressive style bumpstop (rubber spring) is used to prevent bottoming. This allows for maximum travel and wheel speed in the normal range, but prevents harsh bottoming or loss of control.
A whole other discussion is variable rate damping. Many shocks will have different damping rates depending on the shocks travel speed. Usually only available in compression for design reasons. This can provide excellent body roll control with soft springs, which still allowing for a smooth ride at speed.
The point is, that its not a simple matter or progressive, digressive, etc. The shock needs to be selected and tuned for the application. Both weight, spring rate, and road surface/speed. Becuase all of these change with your typical 4x4, you are not going to find a one-size-fits-all approach. Any decent shock tuner can walk you through the options, and tune for the application thankfully.
Right....basically all shocks are 'variable rate'. All shocks are speed sensitive, it is just the slope of the line that changes.....Digressive, Linear, or Progressive.This is a nice graph. A linear shock has the same damping rate of change for its operating area. Progressive/digressive shocks change the rate depending on the velocity. Several shock builders offer external adjustable compression rates. Some have a single adjuster for low speed, some have two adjusts for high and low speed. Which allows fine tuning the compression curve.
As you mention with progressive springs/bumpstops, the reboind damping needs to be proportional. Especially at high velocities (and with high unsprung weights).
If your shocks are good and firm. Try some softer springs. Coils are cheap. Not sure if I'd bother with the trucks leaves.I have Bilstein 5100's on my Jeep and 4600's on my truck. The feel like they are valved way to stiff for washboard or potholed roads. The Jeep actually drives pretty well without the front sway bar, which says to me that the low speed damping is way too high... They do work well for really bombing through stuff though. On my truck, washboard and expansion joint hits are pretty stiff when empty, but with the camper in the back, the ride is fairly well controlled.
I would have preferred a more linear or even progressive valving for Jeep, and linear valving for the truck, but there's no good place to get good valving without spending a lot of money, and often sacrificing travel. I found that Fox shocks have ~1" less droop travel than comparable Bilstein shocks for a given application. I need all the travel I can get with my more or less stock suspension...
Somewhere on here there's a thread about trying to find shocks for my Jeep. Turns out they're all too stiff unless you have 1000lbs of offroady crap bolted onto your Jeep... I think the trend to make shock damping so stiff that it's noticeable when you replaced perfectly good shocks is ruining the ride on many otherwise good vehicles.
Additionally, one of my employers does a good bit of shock sales. The Bilstein shocks seem to hold up. The Fox shocks almost always blow out the seals fairly quickly, even on mildly driven trucks and Jeeps. While I like the idea of spending my money with Fox, I can't justify it with their terribly track record and limited travel.