The value doesn't scale linearly with dimension; the bigger plank you can
get, the more it is worth.
When I was a kid in Oregon, they were still logging first growth, douglas
fir and cedars. I used to carry a baritone horn to school while trucks went
by carrying one log, a piece about 20' long. Those went to a lumber mill,
where planks were cut off. After the core got small (I don't remember how
small) the remaining part was sent to a veneer mill where a lathe removed
layers for plywood. The final "peeler core" was about 6 inches in diameter.
Depending on the mill, those could be sold for firewood or cut up into
broomsticks, etc. They finally burned the bark, chips and sawdust to
generate steam. It was said they used everything but the smoke. And
actually, electrostatic precipitators in the stack collected particulates,
which were pressed into charcoal briquets, although it didn't pay to ship
"and a useable minimum diameter of 6', "