I had WSI HD springs at one time, took them off and sold them when I got the ICON RXT System that included the leaf springs. I added the extra leaf when installing and have been very happy with the outcome. You can definitely feel it working when off-roading with weight in the back. With an empty bed, it is somewhat bouncy, definitely works better with weight.
Personally I wouldn't switch the extra leaf in and out just when off-roading, seems like a pain as removing leafs, taking them apart each time, re-installing would be a pain plus technically you should change the u-bolts each time as they are not really designed to be used over and over again due to the torque to yield.
I sell either brand, ICON or Deavers. @
mstennes , I can do a custom order with Deaver for you at no additional cost for one designed for a heavier load but it takes about 6 weeks or so to ship. Shipping to commercial usually runs between $150-$160 and residential around $180-$195 but would need exact address to provide accurate quote. Send me a PM if you are interested in seeing the cost of either option.