1/2 has been working for our ditch witch (3200#). They do loose there rigidity but I found that kinda helps a little. They still spread the load quite well and as long as they aren’t all broken up (turning and catching a corner in the tracks does it every time).
You could try the adapter but remember that adapter is going to add distance between your lift pins and the load. Not a huge deal but capacity may suffer slightly.
Grabbing with the grapple (BMG or root) works great for 3’ mats (as long as you can have them up off the ground to pick them up) but I wouldn’t do plywood. The power needed to grip and hold is too much to apply without busting the wood up.
We don’t like piling it on the machine either. Too much handling = time/wasted energy = less productivity. And it scratches my pretty paint

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With the forks 2 guys can unload (with our setup) and lay out 20 sheets in 10-15 minutes. Our new mats (because we haven’t got a system yet) took us almost half hour Monday to unload by hand and lay out. I expect 10-15 minutes when we get our new rack built.
Also it’s really nice to have the forks with you. Tuesday we did a 36”+ Pine and the BMG wouldn’t hold the pieces. Threw the forks on and it went right onto the trailer, no issues.