I have the 3 leaf springs.
But you're making an apples to llamas comparison.
The worst choice for hauling with these trucks is a double cab. Best choice is a regular cab.
Reason is that as you add cab between the front axle and the back axle, you push the bed (load area) further away from the front axle. As you do this, you reduce the percentage of the load that the front axle handles. Thus, you are actually increasing the amount of load the back axle handles.
Ergo, with equal loads and equal spring packs in a double cab and a regular cab, the double cab will always sag more.
The truth is that the OEM springs suck less as vehicle length and wheel base decreases, but differing degrees of suck is still suck. In the land of weak springs, the regular cab Tacoma is king.