Next fri. I will start hauling up river. Looked up some weights. Lumber (@ 35 pounds per cubic foot, Douglas Fir)4
2X4 1.28 pounds per foot
2X6 2.00 pounds per foot
2X8 2.64 pounds per foot
2X10 3.37 pounds per foot
2X12 4.10 pounds per foot
4X4 2.98 pounds per foot
6X6 7.35 pounds per foot
6X8 10.03 pounds per foot
One 23/32" 4'x 8' plywood piece would weigh approximately 67 lbs.
One 23/32" 4'x 8' OSB piece would weigh approximately 78 lbs.
Plywood is approximately 15% to 19% lighter than OSB. While the additional weight of OSB does not mean increased strength, it just means that it is heavier to handle on the job. In addition, OSB's higher weight means higher thermal conductivity (thus slightly less R value) than plywood.
Looks like plywood is the way to go.