So what is the big benefit to the YJ springs? My new to me 8 rides a lot tougher than my last one did and I am looking to upgrade. I will need the 4" to 4.5" to clear the tires I currently have.
A wider/longer spring will be smoother then a narrower/shorter spring, spring rates the same for both, supposedly.
The RE 4.5" lift uses the wider 2.5" all the way around. Stock CJ uses 2" wide front springs, 2.5" wide rear springs.
A stock CJ rear spring is the same length as a stock YJ front or rear spring. The YJ front spring is 1"longer then the stock CJ front spring.
So, when using a YJ length front spring, you have to move the shackle hangers forward 1".
Stock vs stock, the YJ's used much lower spring rates then the CJ. But, spring rates are not the only thing that dictates the ride, i.e. teflon pads between the springs, other stuff.
All in all, I am happy with both the RE 4.5" lifts I have on two Scramblers, they ride great. I did add a main leaf to the rear packs on the V8 Scrambler, it was a bit too squishy feeling at high speeds.
I am very happy with the BDS 2" YJ springs/conversion kit on my green Scrambler, it rides great, too.
I do not have direct experience, but a lot of people are very happy with the Old Man Emu YJ springs, too.
As for spring rates, I did some research. This is what I found for various springs. Some came from manufacturers, some off the internet, so grain of salt and all that.
Superlift 1" Springs Front = 285 (5 leafs)
Superlift 1" Springs Rear = 350 (5 leafs)
OME CS036R Springs = 188 (commonly used front and rear)
BDS 2" YJ Springs = 276 ( four leafs)
Stock YJ 87-90 Front = 128/203 (stock/optional) (four leaf)
Stock YJ 87-90 Rear = 170/237 (stock/optional) (five leaf)
Stock YJ 91-95 Front = 113 (four leaf) (that seems petty low, must be 4cylinder spring rate?)
Stock YJ 91-95 Rear = 170 (five leaf)
Stock CJ Front = 170/185 (I know there are more rates then this)
Stock CJ Rear = 230/250 (I know there are more rates then this)
Rubicon Express 4.5" Front = 210
Rubicon Express 4.5" Rear = 224
Like I said, take it with a grain of salt. I do know the BDS YJ 2" springs are 276, I spoke to tech support before buying them. I was concerned that it seemed high, would be stiff. In reality, they are not, they ride really smooth.