My cousin had 6" on his 03 with dual king piggybacks. It rode and jumped very smooth. The key is there are 10-12 thin leafs per pack which makes for a smooth ride vs. other brands that have 6 thicker leafs per pack.
I had a set from Atlas springs on my 95 Chevy that I did a straight axle conversion on. They rode great compared to the springs that they replaced. It was a 6" spring.
I run 8" ICONs........the old ones that used to be Deaver springs and I ABSOLUTELY LOVE THEM!!! they are so plush seriously, it was a night and day difference between superlift and these.