It will be a combination of shocks/valving, spring rate, and tires.

On the budget side of things I have the 6112 with the 600# coils and I think they are much smoother in operation than the 5100. It’s a lot more plush in general than the 5100.

Another option on the high end is getting a shock with adjustable valving so you can smooth it out when needed and still maintain performance for those times you want it.

For tires… a nice set of passenger rated Michelin road tires like the defender ltx m/s and you would be driving on clouds. In my experience I have found tires make a massive difference in the perceived smoothness, especially when doing an A/B comparison between something like an E load and a P metric.