Icon's with 14" 600# spring

I'm sure its posted somewhere in here but couldn't find it. I'm removing my Maxtrac spindles and gusseting my stocks. Removing my 13" 650 spring and and replacing it with a 14" 600 spring. I'm looking to get a 2.5 lift with a softer ride, since Its going to be my work truck now. Question is how much more preload would I need to get 2.5 lift with the new 14" 600 spring. I don't have a Icon spanner wrench, I'm asking so I can have it set at the shop that does the spring swap for me.

 

How did the 600 lb spring work out?