It all depends what the purpose of the step up is.
I immediately stepped up from 600lb to 650lb springs. The former just did not cut it for me either at some speed or when crawling. The 650 firmed up the front in both circumstances. I lost the plush ride of the 600s but the ride is still good, street handling is amazing for a truck, and the offroad performance is all I need.
As others said, any 2.5" coilover would be considered a step up. But what will the purpose be?
If you want to sustain high speeds, then, yes. If you want to adjust on the fly, then Radlfo sounds great.
But I am not sold on the reservoirs, especially up front. Considering I don't need them when I drive 100 miles in the desert in a short afternoon, I very much doubt that most of the people who have them have ever actually needed them. Second, adjustability sounds fantastic in theory, something I have long wanted, but until I decide to do the Rubicon or Golden Spike, I don't feel the need for it. My 1" all around lift gets me just fine on any trail up to that level (and I am sure the Rubicon is doable as is, considering my armor).
Since I have never had the chance to drive King or Radflo, I have no idea how much better they might be on pavement. If King can provide the plush ride of 6112 with 600lb springs on road while also provide the capability of the 6112 with 650lb springs offroad, then that would indeed be a dream come true. But is that improvement worth the cost of admission and the rebuilding? Depends on budget and goals.
If you think you can actually use a race suspension in the desert, it would be worth being realistic: maybe you do, maybe you do not. I have no clue. But I would venture a w--i--l--d guess that few people can really exhaust the 6112 capability.
Remember that if you push that fast, you will also want more wheel travel so it won't be "merely" a 3,000$ upgrade but a super-involved and far reaching LT process.
So the real question really is if anyone can get much out of Kings over 6112s with 650lb without going LT.
That said, if you are happy to spend the money, by all means, get whatever you want. But if money is tight maybe get to drive a King 4R and see if it will make enough difference for you.
