If you are going to be carrying a lot of weight, I would do something custom. Thats what a lot of guys have done (including myself) and other than price, I have yet to see downsides.
I ordered my CSS springs through Deaver using the below specs. A few other guys carrying a fair amount of weight used the same. This is a for a 4runner with 4x4 Labs rear bumper, rear drawer loaded with tools, fridge in the rear, 3 jerry cars etc... When I bought I believe they were around $385.
➢ Load 1,050 lbs
➢ Load Height 13 ½
➢ Rate 240/300 lbs variable
➢ Free Height = 18”"
Diameter: .671
7.625 total coils
Variable rate spring 240lbs / 300lbs