Seconded, go standard. Easier to return if there's a problem (and there do seem to be some quality issues on many springs) as the spec is clear, ride hight etc so you know if they are right or not. Standard work well on LWB and work best when loaded. The friction between the leafs is part of the damping and firms up the the ride to control body roll when there's a load on. Did 75 miles yesterday in moderately loaded LWB on std springs with no issues. Springs could be original (48 yrs) and in the 5 years I've had it there has been no change in ride hight whatsoever.